Both are fine, but I'll stick to 25 HP then (I'll halve the Drow then to reflect this), because as you noted, this fight looks unbeatable as is. I know, this battle is actually meant to be unbeatable in the sense of trying to whittle away her HP. That's because it's not actually a fight, it's a puzzle  ;D You don't have to defeat her or the roper in that way, just find a way neutralize her and get to the next room.