Best medicine for cat's injury?

My adopted outdoor stray has a sore that she has licked raw. I have been putting a red iodine-like medication on it but she just licks that too. My other options would be peroxide or neosporin ointment. I don't want her to get sick from ingesting any of this though. I don't want to pay $200 at the vet but I don't want it to get infected either. What is the best thing to keep it clean?