I don't think she's that out of line. Assuming her story's straight, she got bit (bit, nipped, love nipped - EOS, he used his teeth on her hard enough to cause a mark) not because she approached him oddly, was rough housing with him, or encouraging him to play with her hands, but because she stopped petting him. I'm sorry but I would have probably done the same thing - I don't need to get bit because I don't have the time to pet a dog. My old GSD (picked up as a stray) was so affectionate and bonded to me she used to 'groom' me with her front teeth when we'd relax together - it hurts! More than once it would bruise and sometimes bleed a bit under the skin. Not sure how it is in MX but here at least she'd have the grounds to make a way bigger deal of it - I wouldn't be surprised if someone here would have asked for a free stay, or even sued.
I would put him on a tie out away from her room/high traffic areas as well as discourage her from petting the other dogs. In the meantime, you have something to work on with Delgado