If you have a diagnosis letter that should work, otherwise maybe hosptial records. If not maybe ask them if they have a form that the doctor should fill in.
I think that they won't accept PIP as it doesn't normally say what the disability is or how it impacts you academically such as going to lectures, you say you have mobility but they might not know the reason and if you would need taxi funding or money for a wheelchair accessible room
Hope this helps, let me know if you have any more questions