Have a look at this site:
This woman has experienced remarkable recovery on LDN. She was not bedridden but she was on a wheelchair.
Personally, I have experienced noticeable improvement within a few months. I was unable to walk more than a couple of blocks and now I can walk until my feet hurt. I can even run short distance.
I have MS for about ten years. It turned into SP in 2004, when I started getting worse and worse continuously. I used to be in the situation I described above in December 2004. I started LDN in May 2005. The damage done to my CNS was quite recent and this is why I think LDN helped a lot.
Actually LDN does not repair anything. It completely stops inflammation or, at least, drastically decreases it. If not much axonal (beyond repair) damage has already occured, the body will gradually repair it. I don't know the extent of the neuronal damage of your friend. If it is just myelin, LDN will help her a lot. But, anyway, LDN will prevent any further damage, so she 'd better take it.
In addition, the CNS is very plastic. Dead cells do not come back to life but the remaining ones will try to strech so that they reach each other, bypassing damaged regions.
Please correct me if I am wrong. I am no scientist. It is just what I have understood.
I wish the best of luck to you and your friend.