The most likely cause started with irritation that she licked. This causes a superficial infection (hot spot). The infected skin itches and a vicious cycle continues of itch - lick - itch - lick.
This is commonly caused by flea and tick bites, but also by any other irritation that causes the dog to itch (lick/chew) the area.
Treatment is cleaning it and using ointment. If you have ointment with antibiotics and steroids (Panalog, Dermavet, etc.) it works best. Human OTC 1% hydrocortisone cream or ointment is OK, but often not strong enough to stop the itch.
Bitter apple is a product that tastes bad. It is make to spray on and stop chewing. It has some alcohol, which also calms itching after the initial burning sensation.
Severe cases may need systemic antibiotics and/or prednisone (a corticosteroid).
Let me know if you have follow up questions.
If she doesn't stop, call your vet either for a visit or for medication.