If it's just a few scales or small area, I would wait it out. Clean the area and keep her warm and dry. A clean paper substrate would be best. If it doesn't improve by the next shed (or if it grows steadily worse in the meantime) then it may need a vet's attention.
If it's a significant portion of her belly and/or if there is any nasty discharge associated with it, you will probably need antibiotics to fight it off and prevent a possible systemic infection.
what can i use to clean the area? i dont want to think i know what im doing and mess it up by using something that should not be used on snakes.