For minor wounds, topical antiseptics that are safe for snakes include the Vetericyn ointment (version for snakes-just a little dab, please) or Betadine. If you use Betadine on a snake, dilute it with water so it looks like weak tea- & apply a little using a Q-tip- DO NOT SOAK this snake! -that would likely make it worse.
As I said before, that spot just looks a little infected to me (the red & yellowish colors)- it's healing but it will take time (sheds!) to fully disappear also. What substrate is she on?