I have had to do this several times with non paying bidders but it was over a year ago now since I don't list much.
Your mom should email the person who won, tell her she paid to list the auction and there are final fees associated with that auction. Then she should let her know she is filing a non paying bidder report but it will not have any negative outcome for either account, it is just to recoup all the fees paid. Once the buyer gets the report, as long as she agrees she didn't pay, your mom gets her fees back immediately after that. There is no waiting as long as she does what Renee above says. It will all be okay as long as she files the complaint.