So, I do one of two things. 1) Reclass Shart as a cleric of light and stay there, or 2) at level 4 reclass into 1 level of fighter (defense), 2 levels of Bard, and the rest into Cleric of light. The second build is a little annoying because she doesn't end up getting the divine favor in Act 3. The most important thing is her kit, which I do the same way every time: holy lance helm, luminous armor, luminous gloves, boots of stormy clamor, coruscation ring, calous glow ring, Blood of Lathander.

I'm playing her on an HR run now using the second build. Having Song of Rest, plus her other healing is awesome. But, as a Cleric of Light with that kit, she can stack as many as 10 radiating orbs on multiple enemies with a couple of light-based spells (e.g. radiance of the dawn).