Does she go outside or is she purely an indoor cat? It sounds like it may be one of the allergic hypersensitivity responses that cats can get ( typically called an eosinophilic granuloma). These lesions usually need oral or injectable steroids to help them heal. Topical meds really don't help ( as you have found) as they lick them right off! So she really needs a visit to your vet.
You may find that not using plastic food and water bowls can help prevent flare ups again.
Other things that we may think of less commonly are abscess/infection ( more so in outdoor cats) and a growth.