Christy,
she may have a raging case of thrush, especially the way you describe the tongue condition and the mouth odor. It cause also cause extreme swallowing pain as well. A bloom of thrush is common when taking antibiotics. Is she on Diflucan or Nystatin?

By the way the dental trays fit snug over the teeth - the tongue is not involved.

I can't emphasize enough the importance of dental hygiene. Osteoradianecrosis (literally bone-radiation-death) could cost her a jaw bone removal. Please refer to:
http://www.oralcancerfoundation.org/dental/dental-complications.htm