This is a hardcore bug - a cutscene happens and you engage Ethel in combat (unavoidable) and it's one of (imo) the best boss fights in the EA game - both in design and sequal. It definately hasn't been QA'd enough as the whole interaction is buggy as heck.
Report it as a bug and send in a screenshot/save file:
https://larian.com/support/baldur-s-gate-3#modal
