This disease is a real nasty one and I am so sorry it has hit you so bad, so quick. It is so tough when our bodies don't respond to our brains the way they should.
My ms is mostly cervical (got a few lesions in the brain, but not the Swiss cheese of my spinal cord), so I also get terrible muscle cramps, which my neuro recently diagnosed as spasms due to spasticity (he had previously ignored my complaints), something about hyper-reflexibility due to spinal cord damage. I have found that the baclophen, amitriptyline and neurontin together really help - they don't entirley get rid of the pain, but it is a lot easier to manage. Maybe ask to add a low dose of amitrityline to your meds for a short time to see if it helps, or try a low dose of valium as that can also help.
This has all been fairly recent for you - you may find that you get some recovery of function still (maybe even a lot, who knows), now that you seem stable - it can take a long time - I have heard stories of people getting some function back again a couple of years after a relapse as damage to the nervous system is slow to repair.
The depression is also no surprise - goes both with the disease and finding yourself physically limited and with an uncertain furure - I am on cipralex for that too! I rattle like a box of smarties because of all the pills i take, and that is without the supplements - oh, and Avonex, ibuprofen etc.
I am so glad that you have someone to assist with your disability process, 25% seems a lot, though! I was sent to a neuro-psych by my neuro in preparation for the disability application - I had to draw pictures and fiddle with a peg board. Don't read the report, it will only depress you even more - never realised that my memory and processing of information was that bad! Seriously, mine recommended a program of cognitive retraining, but since I don't know what that involves and it sounds rather Pavlovian, I haven't done it yet...
All in all, you are really having a bad time and having to come to terms with a lot of changes really fast - I hope you do well on the Rebif and that your disability application goes smoothly. I know that you will find some good info on this site - the folks I have met here are incredibly knowledgable and empathetic.
All the best