Weakness

My mother was diagnosed with metastic bone and lymph node cancer, but the primary could not be found. She had two rounds of chemo and radiation, which kicked her butt. She is 77 years young and was very active. We took a break from the chemo and radiation. It has been about 7 weeks since the last treatment. She has been getting a little stronger, but her legs are very weak, and she cannot walk. Has anyone else had this problem or can share any information they may have? Any suggestions or information would be much appreciated.