the above link didn't work for me - try this one
http://www.mult-sclerosis.org/mstreatments.html
MC,
A quick look and I don't see anything that matches up with MS and nerve blocks- Perhaps someone else here will have some experience with nerve blocks.
In the meantime, I pulled up a wonderful reference for pharmaceutical drug treatments for MS that you might find useful - it is available online at
www.mult-sclerosis.org/mstreatments
If she is open to complimentary alternative medicines, I would recommend accupuncture for pain management. She could at least try it and see if it helps at all. I have had several needle sessions and all yielded lots of benefits.
Your mother is fortunate to have you there with her trying to find her some help. I know the system in the UK is quite different to navigate - good luck in getting her something for relief.
mybest wishes to you and your parents,
Lulu