Hi Josephine,
I was "diagnosed" with RSD. It was wrong though and I knew it. It sounds like your sister is in a lot of pain. I think you should consider continued investigation into the underlying cause of your sister's problem.

As you note, medical doctors are not particularly enthused about solving problems. You only have two choices
1) concede and suffer the consequences
2) solve the problem yourself with a thorough investigation

The preferred option of having an expert solve the problem is simply not available, as much as you and I may wish otherwise.

Hope you get to the bottom of it!