Mejis: I effing hate wraiths. They're the one monster that I seem to struggle with.
For this quest, I thought it must have been bugged as I'd fought so many, but then they all finally quit respawning and I'd finished it.
It took a while for Anezka to realise that I'd completed the quest though; she wandered away from the shrine and just stood in the forest for a bit before it would let me interact with her.
On a side note, my tactic was to run away from them and there'd be a point where they wouldn't come any closer, but they also wouldn't attack her whilst she was performing the ritual.
So, I could run in and pick them off, Yrden then/Quen etc.
Still, seemed waaay too many to fight in my opinion without you knowing whether it was bugged or normal.
Judging from the loot on the ground I think I killed at least 9 of them. My quest doesn't fail when the wraiths get close to Anezka. In fact, she seems to be oblivious to them.