Why the fire staff? Its nice when the adds come out, but unless I missed a vulnerability, ice does more damage per eitr and slows.
I beat here just by wearing root chest, tanking and parrying her hits while chopping and then run off to heal using staff. If I got adds, I ducked where she could not get at me to clear them.

I did not use pure magic, I used my normal sword/shield/armor build with 2 health foods and 1 eitr food. The eitr armor and 3 food approach I found leaves you very weak, if you mis-step its over.