I am so sorry for all you have and continue to face. I wish I had words to comfort you. Are you in the program you were going to attend? I know things are different in the UK then US in terms of treatment. Is there any way your current docs could rush things for you to go to the adult like suggested by your mom?
Though the rsd may have spread I do feel there are always treatments or meds to help. I know a girl your age who was in a wheelchair and had to take I think a year off high school. Her rsd spread through her body and she had tried so many treatments/meds and saw so many docs etc. Then finally she found the right treatment for her finished school,is in college,doing physical activities etc.
I know right now it is hard to think that could be you and I feel the same for me but it just takes 1 treatment or 1 doctor to make a huge difference.
I am here if you want an email buddy too.
Sending feel better thoughts