Same bug here. I passed the initial perception check in swamp, so I never even saw the red caps as sheep, but I just left them alone when they baa'd at me. Got to the hut and when I insisted on talking about Mayrina the fight triggered. Ethel immediately went behind the fireplace and disappeared. I killed all the Red caps, went through the fireplace, went through the door without wearing the masks, killed all the mask wearers, and when I reached the cage room the bug happened. I never even really had any combat with Ethel. She changed, fled downstairs, and I never saw her again.