As I mentioned, I tried healing her with a spell first. But some fiddling around with older saves helped me pinpoint when I offended the NPCs. Not sure how disarming the gas traps in the cave behind the druid grove got the *tieflings* angry with me, but at least I figured it out.
Sorry, I homed in on the potion chucking bit and clearly didn't read the rest of your post carefully enough!
But it's great you've worked out what the trigger was, though extremely weird as you say. At least it sounds repeatable, which should help Larian diagnose and fix the error. It's perhaps worth using their support form to report the bug and send them your save file, if you haven't already.
"You may call it 'nonsense' if you like, but I've heard nonsense, compared with which that would be as sensible as a dictionary!"
