I found her much easier the second time around; I hit her before she could finish summoning (warrior character with the passive Stun skill maxed), so she kept retrying that and never moved on to attacking.
Did your character get blinded? Hell Spikes should have still worked then, though. Try using a shadow potion to take a break and set up for another attack (a warrior character using their special move will not turn visible if they don't direct target a nearby opponent).
Burning wall can be very effective, if you have it or spare skill points.
That's probably the best tactic you may not have seen already in topics like
Chasing Josie...
