My dad underwent chemo and radiation. It took a lot out of him. The chemo made him very tired and the radiation made him tired and weak. It is important that your mom get all the rest she can in between these treatments. What she is experiencing sounds normal. I remember dad sleeping all of the time. The side effects are strong, he got very weak, very pale and had no appetite, but he made himself eat. Soon the chemo and radiation will be over and she will regain her energy. Dad did, he felt much better about 2 weeks after treatments ended . Unfortunately his lung cancer came back about 6 months after treatments, it went to his bone, then to his lungs and within 6 weeks his lungs had mets everywhere. He is going downhill fast now. He is at the end now, just waiting. This major downhill just hit on Sunday. Saturday he was outside watching his grandchildren play. It's very difficult to deal with. Lung cancer is ugly, and just when you think it cannot get any worse, it does. For now just look at the positive, and take one day at a time, after the therapy, she will have some good days, dad did, and they were some of the best days we sharred as a family. We had about 6 months of great days after his treatments, they really were the best. Keep this in mind, and when your mom is done with treatments she will feel better, enjoy every minute you can with her, life is too short.
My thoughts and prayers are with you and your family. My family and I have been through this part, if you need guidance in the future, please remember me as we have hit this milestone in the disease, and are now on the next step. Please keep us posted.