I'm not sure what to do. It is quite obvious that the "Mayrina" with the lower hit chance is Auntie Ethel. If you cannot see it and the result is random, however it may just be an incentive for save scumming. I would leave it as it is, probably.
Maybe not that much needs of save scumming as a result. Bcs by the time Auntie mimics Mayrina, there might still be one or two of her illusion copies around for the player party to spend their action points and maybe drink a potion or two. Too bad I haven't see Dispel Magic around, but letting a low str companion to throw something light weight might prevent accidentally dealing lethal damage on true Mayrina. A spell of Sleep would probably help telling which one is which since the real Auntie probably quite "immune" to that spell.
BTW I always kill Auntie Ethel. She is the only really evil creature in the game. Other than the Goblins, Drow, Duergar etc. she has no factual agenda and goals other than her pleasure with torturing and killing. I would throw out anybody from the party who showed the slightest doubt what to do with her. On the meta, I would delete the game from the harddrive if you had to support her. Mayrina on the other hand loves her husband. I can understand and always help her.
More likely a chaotic neutral being to me: she is as providing as the mother nature herself, and as merciless as the mother nature herself. Gale talks about some mortal's folly, and just like Karsus and Gale, those who seek help from that hag had each their own kind of folly. She is the type that as long as you don't cross her nor obsessed on something, then you will be fine. The tiefling nanny had her pot setup right next to Ethel's, yet she was left unharmed. So does the rest of tieflings and druids, except for the one on warehouse guard duty(but she will be fine, any priest in Baldur's Gate can cure her). If you reject her offer, she just won't push you. Will the Absolute and its agents do the same? Those are the really evil creatures in the game. Auntie? Only half evil as them.
