What Causes Dry Mouth And Discomfort In The Gums?

Hi..my 90 year old mother has had a problem with slouching of her gums ahd lips inside where she feels little strings of skin membrane which she cannot cut with her teeth and it is very bothersome feeling. It is progressing and she asks the primary care who has no idea, she has gone to dentists who say it's dry mouth, but I and my brother have been diagnosed with dry mouth but do not have this feeling. My mother's labs are ok. A problem stated when she was taking a bl pressure mediation for years (Lisinopril) and then all of the sudden she got an anaphyastic reaction from it and was taken off