My spider actually has 2 wounds that are very similar to that, He also has a pretty big one on his head rom rubbing. I posted this on another thread, but it applies here as well
My guy was rubbing and has a wound on his head, and under his chin. I had been cleaning it and putting neosporin on it, but 3 months later it's still not healed and a little worse (not horrible, but worse).
So he went to the vet (Dr. Kevin Fitzgerald) and he said that it was a little infected. That BPs have a lot of different bacteria on them that are very opportunistic, so that BPs are slow at healing. My guy got an injection of antibiotic (Baytril), then I give it orally once a day and clean the wound and apply the cream (Silver sulfadiazine) once a day. He said the SSD was better than a typical antibiotic because it creates a very bad environment for the bacteria, but is safe for your snake.
I would take her back in and do what your vet reccommends.