Hi and sorry to hear about your mother's experience. My father completed radiation therapy in May (35 treatments) for tonsil cancer and opted not to have the feeding tube. He is still unable to eat, due to throat pain and the horrible "metalic" taste that is present. He is currently trying to force down 4 Scandishakes ( a high calorie shake mix) a day --mixed with whole milk and ice cream. These take him a good hour to get down. He is also able to manage some broth. He has lost 30 some pounds to date and cannot stand to lose any more. He turned 71 last week.
Looking back to pre-radiation treatment, he had the option to have a tube placed, but chose not to , thinking that the side effects would lessen after completion. But unfortunately, they are still affecting him and he is miserable. He has a doctor's appt. this Tues. and they may recommend a tube, and he will probably go thru with it.

My advice is to discuss the option again with your mother. Things are going to get worse for her, before they turn around. It has been a horrible 4 months for my dad. I only wish we could have seen in the future, and maybe he would have opted for the tube at the get go! Prayers to you and your mother!