First of all, are you 100% sure that the wound is because she keeps scratching? If she is, you have to make sure she doesn't have fleas or allergies. Allergy causes a cat to scratch constantly, and it may be caused by anything, from food to wool, to any substance or flea collars. The cat will immediately start scratching until the skin gets irritated.
Don't put cortizone on the wound. Triple antibiotics will help keep the wound from drying out and prevent infection of the wound. Malacetic works well for cleansing the wound. But please don't just assume a wound isn't painful. Keep a close watch on your cat. If she keeps scratching or if the wound doesn't heal, take her to the vet.
Please don't. The medication isn't meant for cats; there are ingredients that are contraindicated.
Your best bet is to go to the local pet store and pick up a medication like "Fungaid", which is designed to prevent topical skin infections. It's not very expensive (about $5.00) and is a much safer choice.