Is she getting radiation as well? Chemo alone would be an unusual approach for Stage IV cancer...

Radiation will also cause mouth sores, in fact it is the major cause in most patients as many oncologists do not use 5FU.

Has she been tested for human papilloma virus? Tonsillar cancer is considered by many to be a "surrogate" for HPV-caused oral cancer (although not all tonsillar cancers prove positive for the virus). However since it has major implications for response to treatment and prognosis, it would be good for her to request such a test.

Gail