So I really don't know that therapists are qualified to do this...but even if you were seeing a psychiatrist not all of your caregiving psychs will write letters etc. for you. It's sort of a dilemma for them becuase they have the perspective that they are getting you better and that you aren't disabled etc. Someone more neutral is better at assessing you when it comes to disability etc becuase they have no stake in the outcome....your personal doc is heavily invested in getting you to be as functional as possible. Anyway you may have to pay someone for an independent evaluation.

Here is a convo about this type of letter....among pdocs on sdn...

Disability Request on Initial Visit | Student Doctor Network