The first thing we want to do is completely rule out fleas as a possible cause to her excessive licking. If there is no chance of fleas or you are not seeing any then I suspect you are dealing with allergies. In many cases an allergic response this severe will respond best to a steroid injection given by your veterinarian and then a diet change to a hypoallergenic diet. I particularly like Royal Canin HP23 for cats with skin allergies. Response to a food change may not be seen for up to 4 weeks this is why a steroid injection is recommended from the start. It will provide near immediate relief. It is difficult to determine the allergen that is affecting your cat but in many cases it is caused by a meat protein like fish, egg, or poultry.
I suggest trying this route first. If a trip to the vet is not feasible at this time then you can try benedryl at a dose of 1 mg per pound twice daily. This is an antihistamine and can help to improve her condition but just doesn't work as fast or as well as a steroid injection will.
Please let me know if further assistance is needed.