I had 35 radiation treatments (on a TruBeam machine, so extremely focused and precise beam) over the summer for a recurrence of poorly differentiated thyroid cancer in the soft tissues of my neck. The treatments avoided my trachea and did not implicate my jaw or mouth, so I did not suffer the worst side effects, apart form some minor neck burn toward the end of treatment. But the single thing that saved my throat for 8 weeks was MuGard, which, if your insurance company pays for it, is a godsend. At my treatment center, the Radiation Oncology team gave it to patients for free when their insurance company would pay. My insurance did pay (I paid $50 for two large bottles and four bottles lasted through the 8 weeks of treatment), but if insurance doesn't it is apparently very expensive. Ask your team if they have access to it. Also, I was entirely compliant with everything the team asked me to do, from swallowing exercises (3 times per day, 7 separate exercises) to twice daily swigging of MuGard, to avoiding all citrus foods and the like. The upshot was that I had one day of discomfort in all that time, and it was my own fault for, early on, eating a spinach leaf that scratched my throat. It's sometimes easy to forget that radiations cooks us on the inside. But I never forgot it again. All the best to you and your sister. She (and you) will get through this.