Is there any ill-fitting denture in her mouth or a broken sharp teeth?if yes remove that tooth and replace that denture.

Ulcers and be for many reasons Few are listed below Loose denture Constant irritation from Sharp teeth Can be a result of habit of keeping tobacco Identify the reason For above two reasons I can ask her to apply any ulcer ointment like t lac,oraways etc For the last option I need to visit the dentist at the earliest

Long term ulcers which are not healing are a cause of concern and require evaluation by a doctor.