When she goes into an almost trance at the end after being teased, she's given a set of powers that basically makes her unbeatable as she can act and block before your character can, and her healing spell out performs even shockbolt. At best you can just stalemate her when that happens so that each of you gradually heal. I can only get two of the endings and I suspect it's because I reached this part of the game that's seemingly impossible to progress past.
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You can get all 6 endings by following this guide if you want: https://steamcommunity.com/sharedfiles/filedetails/?id=1632648905