Thanks for the excellent photos.
So sorry your mom is in so much distress at this time. These are very painful and upsetting as well.
You are correct that is a canker sore or sometimes called a Recurrent Apthous Ulcer (Stomatitis).
Canker sores are a result of either, stress, a poor diet, a vitamin deficiency, food allergy, smoking, just to mention a few. They are usually gone in 10-14 days with or without treatment.
You can use one of the following remedies: Benzocaine , Oragel , Lidocaine or
Triamcinolone dental paste .1% also known as Kenalog in Orabase. This is a
topical corticosteroid preparation (granular paste) with pectin in it that allows the ointment to stay in place even in the presence of saliva! Your dentist or physician can prescribe this for you to have on hand if you get canker sores often. Use it sparingly about 3 to 4 times a day.
Another anti-inflammatory paste called Aphthasol is also a good remedy for canker sores as is Canker Cover. Vitamin B complex and Folic Acid have also been shown to be effective in reducing canker sores.
You can also use salt water rinses: you can dissolve ½-teaspoon of salt in 8 ounces of water as hot as can be safely tolerated, and rinse vigorously for about 2 minutes at least every 2-3 hours or diluted Hydrogen Peroxide rinses.
Does all this make sense to you?