Paladin/cleric is good! A pretty niche build that I always like is 7/5 light cleric/vengeance paladin, it’s basically a light cleric with divine smite and double attack. Focus on wisdom since paladin’s spell list isn’t that useful.

If your initiative is low, you can consider taking hellrider’s longbow for an additional +3 initiative, or picking up the alert feat, which is one of the most busted feats in this game.

As for items, sacred star/blood of lathander/selune’s spear of evening are all great options. You can basically equip her with all the items that mentioned radiant orb and you’re good to go.

Respeccing Shadowheart to Light Cleric after the Nightsong gets resolved that way is a Respec I would allow at my table. It makes sense from an RP stance.

Paladin/Cleric is a great multi, though usually you usually take Paladin to at least 5 for two attacks instead of 1. Which class goes to 7 is a toss-up. Cleric for more spell slots, thus more Smites and more Spirit Guardians damage, or Paladin to 7 for aura. Either is good.

Party comp sounds good, and it sounds like you're having a lot of fun with the run. As a fellow Arcane Trickster enjoyer, mind if I ask how you have Astarion set up?

I use life, and it's a bit ridiculous. With the right gear, her heals are insanely efficient and buff her chance to hit. Keep spirit guardians up all the time, add war caster and the highest ac you can get her to make her a high priority target that's hard to hit. She still does respectable damage but the impressive bit of that spec is the amount of damage she can mitigate.

Aiming for full 3 feats, so if multiclass will be 8-4 or 4-4-4

War cleric can be helpful if you want her to be a bit more of a Frontline fighter

A lot of options for Shadowheart. If you are thinking of Storm Cleric, you might multiclass it with Storm Sorcery. I have heard taking 2 levels of storm cleric with the rest going to storm sorcerer to be very powerful.

Another option is to make her a light cleric which is especially helpful for Act 2.

I'm not a fan of dedicated healing builds either. My top 3 favs for SH are:

1. Gloomstalker 5/Trickery 7, archery focused build, can carry Phalar Aluve or Sorrow. I got Harold ASAP, and she used that well into Act 3 to bane a group of enemies with arrows of many targets.

2. Tempest Cleric/Storm Sorc, various combinations, can start with sorc for mobility or cleric for heavy armor. Very damage-focused build but less lore friendly.

3. Nature Cleric - overlap with druid, good control spells, can use torch with shilleleigh in the early game. It doesn't fall into the domain of her goddesses, but it suits SH's personality.

I'm a big fan of one-level Monk dips on Clerics, and on SH in particular because it lets you build around her spear (whichever you end up getting) without sacrificing spellcasting and with the option to wear robes.

One of my favourite Selûnite builds was a Knowledge 5/EK 6/Monk 1 with GWM/PAM/Sentinel. Add Khalid's Gift, Diadem of Arcane Synergy, Bonespike Boots and either Moon Devotion Robes or Robe of Protection and you get a very solid melee.

I’m cooking up a trickery 7/fighter 5 build with shar’s spear and my melee gloomstalker durge wearing bhaal armor, I have to pump her with giant elixirs so she does damage, but it’s working fine so far. The cleric utility is a huge plus and extra attack gives her more juice

I did that build on my first durge character and it was a lot of fun. Using necrotic spirit guardians allows you to still use shadow step because it doesn't generate light like the radiant version does.

I did the shadow monk thing as well similar to you on a solo playthough. I felt like the Cleric part wasn't really doing a lot, so I just dropped it and instead went Shadow Monk 6 / Thief 4 / Fighter 2. This felt great both as a coherent build that could solo the game and as a thematic choice for her.

Alternately the healing build IS a fantastic damage build - Sorc 1 / Cleric 11 and build for Rad Orbs/Reverb. I've also done a solo run with this build, so it certainly does the damage we need at all stages in the game (I was worried about Myrkul, but it didn't end up being a problem at all).

Upcoming patch 8 will let you improve this with 2 levels in druid to ensure you never lose concentration.

One build I came up with was:

Life/Knowledge 5/EK 6/Monk 1 with Sentinel/GWM/PAM

Core gear: Selune's Spear, Selunite Robe, Dex Gloves

Cleric/monk does indeed work and is extremely good. 6 Open Hand 6 Light cleric is a very strong reverb build and is just delightful to play. 6 OH 6 tempest is great also for knockback punches and Call Lightning burst. 6 shadow monk 6 trickery is excellent also but is much better aligned with SH's evil/Shar path. Can say more on any of these if they sound interesting.

Cleric/paladin can work, but is quite multi attribute dependent. Works best with either DEX/STR gloves or STR elixirs so you can get to 16 in both WIS and CHA. One of the better versions is 6 vengeance 6 war cleric, with a reverb focus, or even 10 war 2 paladin as a hybrid support/damage build. In both cases Phalar Aluve is probably your best weapon, and concentrate on Hold for autocrits or Spirit Guardians for more passive damage/reverb.

Im old school i like my healers, pure life cleric is amazing suport and control

The narrator implies it's seluna that gives shadow heart her strength after pivotal plot point. So any good or neutral aligned domain makes sense

I use her in almost every playthrough. In my opinion, the strongest build is to stack ALL of the items that proc when a character heals someone. That's the helmet from saving the Grove, the gloves from the tiefling leader, the ring from Volo etc.

That allows Shadowheart, with a bonus action and a level one spell slot to heal the target, heal herself, give the target blade ward, give the target bless, give the target a free disengage etc. You can basically turn her into an insane value machine.

In a pinch she can cast guiding bolt and necrotic touch and do massive damage as well. Mace of Farie fire to give advantage to companions. And her AC is pretty high with a shield.

She's basically just THE BEST support character.

I save her spell slots for inflict wounds or guiding bolt. I use potions to heal instead.

I always place down invoke duplicity for advantage to attacks first, then I just keep casting inflict wounds (3d10) on the enemy with the highest hp.

I don't bother wasting spell slots on low hp enemies. I just attack with a torch to help out a bit and make sure no one is obscured by shadows.

She’s my Bless bot. I give her all the items that buff her healing (but only because there isn’t much else for a cleric right now), and take the +2 Wisdom at level 4. Weapons are Spear and Shield.

During fights she casts bless and in later rounds spams guiding bolt, or inflict wounds with the occasional melee or crossbow attack mixed in if the fight seems to easy to waste spells on. A healing word every now and then should someone go down.

i just spam guiding bolts...

FYI, healing is not meant to be a primary action in DnD. The most effective way to prevent damage in DnD is kill the thing doing the damage. Spell slots are just too valuable. The one exception is healing downed teammates so they’re back in the fight. That’s what healing word is for.

What clerics are best at is buff spells, like bless, and AoE damage (spirit guardians is one of the best spells in the game). If you don’t have another character with enhance ability I think you should bring shadowheart.

The only exception the healing rule is life cleric, which can put out MASSIVE healing with its channel divinity feature, and combined with some magic items that turn healing into buffs, it can make honour mode a cake walk

Bring her to withers and respec. She can be a great healer

Respec her as life cleric, profit

I've been trying Shadowheart as a Valour Bard because I've never tried it, and gave her a level of Wizard so she can learn even more spells, and it's been pretty fun. Not optimized, but it's an evil multiplayer run, so no Karlach. our group is a Vengeance Pally, Spore Druid, Assassin Rogue, and WizBard and we're pretty OP.

Oooos I’m romancing Lae’zel is not a consolation prize. It’s a great story.

Respec from trickery to light and then you'll never want to be without her in the party

For act 1 at least, I like having her equipped with the luminous armor (look up what that does, it's kind of broken) and then load up with radiant-based attacks to exploit that armor's ability.

Later on her Spirit Guardians can also be pretty helpful for crowd control (helped a lot in a certain boss fight from her personal quest, where she was basically a one woman army), and some of the level 6 spells (like Blade Barrier) made act 3 bosses stop in their tracks.

Light is where it's at for a first playthrough, IMO. Nice balance between party support and offensive power.

I'm running her as Life for a second playthrough. Seems like a solid choice if you want to lean in towards pure support.

Trickery Clerics kind of sucks generally speaking unless you want to be super clever with stealthing around or something, make her pretty much any other Cleric besides Knowledge (as that's for skill monkey stuff then combat) and she'll be better for you most likely.

Though Clerics have great offense that you should consider leveraging, Guiding Bolt, Spiritual Weapon, and Spirit Guardians are great spells when you get them and the latter two stay good pretty much forever. For a newer player I'd suggest playing Light Domain, it's just free utility in Warding Flare and extra damage options with Fireball to pair with Spirit Guardians. Life is also fine if you desperately want a heal bot Cleric.

What level are you? This would help.

Open hand monk? Will synergize with your short rests nicely and it's pretty damn powerful. Probably have a bunch of unarmed junk sitting around i would guess.

Light and Tempest Cleric are fun. Death Cleric looks like a blast too

I know you said she was already a light cleric, but if you dip just one level into storm sorcerer, she can fly. Your rad orb build + spirit guardians + flying is a super powerful build, just fly over all enemies and tag them with damage and a few stacks of orb

1 storm sorc / 11 light, life or tempest cleric

Light Clerics are fun, but as they use a lot of resources they rely on rests.

I had a lot of fun with my Radiant Poisoner build for Shart.

It's a cleric / thief with a lot of mobility and debuffing enemies with RadOrb, Reverb and Poisoned. It does decent damage, but it actually makes everything easier for the team.

The mobility with Spirit Guardians is something really underestimated until you see the impact across the battlefield.

Any radiant orb stacking build works great as a support, and is thematic for Shart

Probably not the strongest, but I like Nature Domain Cleric.

Spike Growth is really nice to slow enemies down AND deal heavy damage to enemies moving through it. Combos very well with Hunger of Hadar, as Blind enemies cannot jump out of it and they take a lot of damage every turn.

Plant Growth slows them down even move (1/4 speed!) and needs no Concentration!

Lashing Whip cantrip is nice to pull enemies to a Cloud of Daggers, Darkness or sometimes pull them off ledges.

tavern brawler monk

but for support cleric, Life Cleric is obviously the best, had good items with healing synergy, like the hellrider's pride or The Whispering Promise (both obtainable in early act I btw)

as someone else mentioned, Nature Cleric is also cool for support and as a bonus: in older edition of the game, nature was a domain Shar worshipper could pick, so it's somewhat lore accurate

For Clerics, Tempest is the highest damage. Using create water to wet the enemies, an upcast L5 Call Lightning w/ destructive wrath is doing 100 damage by cleric level 9.

12 Light cleric IMO since with this you can face tank with her as well as doing great CC, heavily item dependent tho, Use all the radiant orb and reverberation equipment available with this she will be unstoppable even on tactician. Cast Spirit Guardians (Radiant) go near enemies and they are basically useless