What Causes Muscles Deterioration?

My 67 year old mother has had multiple back surgeries to her lumbar spine due to degeneration of disks. The most recent was a month ago for a T3 spur. Additionally, she has seen several doctors for right hip pain. Starting about two months ago, she has had a rapid deterioration of her right thigh with intense groin pain and even some problems with her rectum. Her hip pops and cracks very frequently. Since her surgery she has had 3 rounds of steriod therapy. While on steriods, she is able to walk better (but still with a lot of difficulty). Her steriod therapy was complete on Tuesday and by today she is in the bed with excruciating pain. She is not someone who likes pain medication at all. She has probably 6 or 8 bottles of unused pain meds in her cabinet. She has been on neurontin and her neurologist is now starting lyrica. Her MD is very concerned and perplexed. He is doing consults and multiple tests. Her nerve stimulation study did show old permanent damage in the T3 area, but no new damage. We are desperate for answers. I have watched my mother that exercised 3 to 4 times a week last winter to a woman using a quad cane to ambulate. I have done some research and I am an RN, but I don't have a neuro background. I have found things about the psosas muscle, etc. I feel like the problem with her hip and leg are related to her back, but a separate problem. What would cause the muscle to deteriorate so quickly? She has had multiple MRIs and CTs with and without contrast. I feel like something should have showed up, but the reports don't seem to show anything. Should we be asking for different tests? Any advise would be greatly appreciated. Thank you.