Her tank looks clean, don't worry about that. I don't see anything that could have led to this. Can you post a pic that shows the rest of the enclosure ? Has she been out roaming around at any time in the last couple of weeks ? Do any kids take her out unsupervised ? And yes ,beardies don't feel pain the way we would like if some of our skin was ripped off, they are built for a tough life but you still want to heal that up ASAP and start with the honey.