It could be Bacterial shell disease which can be caused by a bacteria or Burn spot disease, caused by a fungi (I think). As for medication, I don't know what would work or if it would even be safe to use.
Really? She moulted before and it didn't disappear...
So dose melafix and remove the moult? The Tail Burn hasn't gotten any worse, but I'll dose anyway. It should work good because I just cleaned my tank and she's the only tank inhabitant.