I had this exact thing happen to my little boy a while back, what I did was get some betadine a a local pharmacy, dilute it with water until it was a light tea color, and dab it in the area with a q-tip every or every other day (depending on how well she takes to the routine) In the meantime, keep your tub super clean, I would consider switching her off of any loose substrate and on to paper towels for a little while. While this scab looks a bit bigger than the one mine had, chances are good that she will shed out of it. Give her a shed or two on this routine, and make sure that the site isn't hindering her eating. If it is, or the issue remains after a couple sheds, I would take her to a vet. Best of luck, hope she gets better!