How Can Leg Pain Related To Ovarian Cancer Be Treated?

My mother has Ovarian cancer . she has completed 8 rounds of Taxal carbo and avastin as of feb 6th. Now we are dealing with severe pain in her legs. She can not depend on them to hold her up. She has been in the hospital to manage pain for 15 days and is now in a skilled nursing facility for Rehab. Her pain is manageable with 125 fentanyl patch and diluadid as needed. (about every 3 hours) We have seen her oncologist , a neurologist ,spine specialist and a rheumatologist no one has been able to identify the source of her pain. She has Had MRI s CT scans,x-rays, petscan, her inflammation markers are up and her thyroid is way off. The PT says it is like someone flips a switch and my mothers legs give out 30seconds later they work fine. they can t predict when it will happen or make it happen.