I really can't see the picture very well but I think it's likely that it's a piece of stuck shed on the mouth. Mouth rot is inside the mouth. See if you can pull it off with your fingernails or a tweezers.
Aliza
Sorry, the picture quality turned out kind of blurry. I tried zooming in on the spot a little bit. If it helps, I fed her earlier tonight and it didn’t seem like she’s lost her appetite, so I’m hoping that’s a good sign! View attachment 50181