I think she bugged in my playthrough as well. I killed her in the tea house. She summoned some redcaps, said her "Bye-bye" words but she did not leave. She did set 2 members on fire and things were looking grim. I (as a player
) panicked, used wyvern poison and dealt more than her left 70 points at once which killed her after one full attack round.
I did enter the fireplace with her around, though, so this is where I started the fight: my party was split between the teahouse and secret passage. That or the witch bolt on her might have triggered the bug.
