What I did was I placed 4 traps (Iam soloing and am a mage/thief) and then I killed the last vampire in the coffin and I just watched while she was getting killed by my traps
I also had 6 lvl summoned creatures to whop her ass if she survived the traps.
I think she got like 2 or 3 hits by my summoned creatures.
I won her on the first try