Hows her white blood cell count? I had a friend that was on Cisplatin and she got really bad mouth ulcers from the chemo because her white blood cell count was down and they gave her the neulasta shot for that and it cleared up her ulcers (she wasn't getting radiation). But, the blisters in your mothers mouth may just be related to the radiation and in that case maybe you could get some magic mouthwash from the doctor to numb her mouth so she can keep swallowing. When I first started losing my taste early on in treatment it was related to thrush - and it can be miserable, so maybe your doctors could look into that as well? There's a million things that it could be but your doctors can definitely do something to make it more bearable for her. Hope this helps some.