Anyone ever experience this medical mystery?

For seven years my sister has had severe, crippling pain in both legs. As if you ran five marathons , she described it. Plus, twitching also in both legs, it never stops. She's had every test done, every blood test, neurology etc. there's nothing that shows up. She now has neuropathy in her feet too, but two doctors have said the pain and especially twitches in her legs aren't typical neuropathy symptoms. One neurologist did believe that her leg issues is also neuropathy.

She's had a couple pain meds but they didn't help. I know there's many more however. Anyone ever hear of this mystery in her legs?? She can barely walk it's so bad. Thank you ♥