HI there... chemo alone will not cure oral cancer. That's first off... radiation... a second round in conjunction with chemo should be given, possibly Erbitux. It sounds like she is very weak, though so proper nutrition is a must. If the cancer (assuming this is what it is.. the only way to know for sure is a biopsy) is still localized, then they are letting your mom die for no reason.

find another dr. willing to treat her... pump up her nutrition, high protein foods, fresh veggies, after radiation people's mouths are very sensitive and ulcerations can occur easily - make sure it's cancer. good luck.