On my very first attempt.. I kind of assumed that the masks were needed to pass the door. Hells, was I wrong. Regardless, I checked the debuff, and it said; "Lasts until caster is dead". I tried to sneak past them, kill Ethel and save her captors... but then Ethel never spawned. Going to try again on my next playthrough.
Oh, I had the same bug happen. She does spawn, but is always invisible in the beginning of the fight. What's supposed to happen is... you walk in her vicinity, she does her little speech and attacks. But that scenario is a little bit buggy right now, basically she's on that tiny bridge close to the orb, if she doesn't do her little speech you have to draw her out by using aoe attacks on that bridge (drop acid cantrips on that bridge or alchemist's fire bottles), it will make her drop her invisibility, but.... in my case she didn't attack me back. She just stood there and took the beating.
Definitely Larian should fix that fight.
