Tips for Shadowheart
Use her big concentration spells. Bless is a very good early one. Guardian Spirits was a kick arse one in Solasta but I’m not sure it’s that good in BG3 ‘cos I think your party will often be too spread out. But it’s still very good if Shadowheart is up with your melee. She gets a lot of other options as she levels up and they are very powerful.
Respec her from trickster cleric into life cleric which is more useful in combat.
Shadowheart is a buffbot and healer who, equipped with mace and shield can also make a damn nuisance of herself blocking/engaging enemies as well. She doesn’t need to actually hit them, she can cast spells instead. She can spam guidance on your big hitters for example. This alone is enough to justify her position in the team.
But when you need that extra bit of damage she has Guiding Bolt. Not only does this do a lot of damage it also increases the damage of the next attack made on that target so it’s excellent for bursting down the tougher more dangerous opponents.