Right now i think shes usually very bad. She works the same as the item that doubles a targets soulburn. But she deals no dmg and takes a really long time to attack.
My suggestion:
Make vestas text be:
“Apply 1 souldburn. Trigger soulburn on hit targets.
Barrage.”
This essentially serves as a “double soulburn” but by triggering it and doing something now.
If this is way too good, then alter her stats or make it 6 turns to activate?
Or lower her hp to 6 to make her more vulnerable