Hi.. Can understand your concern.. As per your complain Canker sores also known as Apthous ulcers occurs due to a number of reasons although the exact reason for its occurrence is unknon still.. Although a few factors a considered as causative agents for canker sores, which are: -Acidic, sour and spicy food.. -Nutritional deficiencies like Vitamin B12,cfolic acid and iron. -H.Pylori infection. -Allergic reactions. -Hormonal changes like during mensuration and menopause. -Stress. -Poor Oral Hygiene. -Immunocompromised conditions like HIV, uncontrolled Diabetes. -Radiotherapy and Chemotherapy for cancer. -Denture wearing. -Allergy to certain toothpastes etc. Although oily food has not been found to cause canker sores but it taken very hot and with spices can be a factor.. H.Pylori infection which causes peptic ulcers in stomach has been found to cause canker sores and as your mouth has been exposed to it you should get a checkup done to find out that whether it is still becoming active at times and causing canker sores. She can takes nutritional suppliments like a multivitamin tablet daily for a month to fulfil for any nutritional requirements by the body.. Avoid hot and spicy and sour foods.. Maintain a good oral hygiene.. Use alcohol free mouthwashes.. Do warm salt water rinses on daily basis once a day. In case if any underlying disease is ruled out you should get it treated and it can be helpful in reducing the frequency of canker sores.. Hope this information helps.. If you find the answer helpful kindly write a positive review and click on found this answer helpful as a token of appreciation.. Thanks and regards.. Dr.Honey Nandwani Arora.