Heather, Please talk to your mom when the moment is right......
We have been through many cancers in our family, and radiation does not hurt and will make a huge difference. What they are telling you preliminary is very good, and they have seen so much they are usually right on, but radiation is not painful and will make a huge difference. My mom had, and lived 30 years past, and another who denied radiation passed away soon. Radiation doesn't hurt at all and is an extra precaution which only takes about a half hour out of your day. Take the walk with her and support her, you will grow even closer, but remember to always encourage her and grab the extras like radiation. Turn it into a day out for lunch, any doctor visit or treatments, and treat it as a positive time to be together.