My 16 year old son gets them frequently too and has for several years.....while I don't know the cause I can give you a couple tips to help relieve the pain for your daughter......
1. make sure her toothpaste DOES NOT have SLS (sodium laurel sulfate) in it
2. have her swish with Scope twice a day everyday during her flare ups.....
these tips help my son. The ulcers usually come back but doing these 2 things seems to keep them from getting so bad!!
Hope this helps.....
Lisa
=)
Could be from dental hygiene to your diet. Sometimes vitamin deficiencies and other times it's nothing. If your worried see a dentist or doctor. I wouldn't get stressed out over it though.