When encountering Auntie Ethel in her lair, sneaking to the control orb first, activating it, and then talking to Mayrina results in Ethel not spawning and Mayrina to be stuck without being able to actually talk to her.
Ethel is actually there in this case, she's on the small wooden bridge close to the orb invisible and bugged. AOE's will reveal her but she likely won't attack back. However killing her should allow you to advance the quest with Mayrina. Sneaking into that encounter bugs out Auntie Ethel, if you want the real fight you have to walk in loud and proud.