Betty, your willingness to be there for your sister is sure to help and be of great comfort! Yes she should stay on top of the thrush, besides contributing to pain and sores, it can develop into more serious problems. Yes you should let her do what ever she is willing and able to do. Physical activity helps the mind and the body to heal (my opinion at least). Yes it probably will get somewhat worse for her but she will get through. Lastly, the appearance from the outside might be unsettling until you realize the beauty and positive changes on the inside that can happen.

Take care

Mark, 21 Year survivor, SCC right tonsil, 3 nodes positive, one with extra-capsular spread. I never asked what stage (would have scared me anyway) Right side tonsillectomy, radical neck dissection right side, maximum radiation to both sides, no chemo, no PEG, age 40 when diagnosed.