Yeah, Lohse is weird like that. If you don't care about everybody else's attitude in the cave, you can side with Lohse, and then get her health low enough to "knock her out of it". That will actually give you a positive gain in her attitude, but all the elves will be -40 or so. Taking all of her armor off before the fight helps with being able to snap her out of it before she hits one of them.
I do agree that siding with the elves shouldn't harm your attitude with Lohse, as you're just trying to repel whatever's possessed her, and helping her regain control over her body in doing so.