In theory, I think, if one NHS treatment doesn't work then the person should be offered the next, it's called a stepped approach.

In practice not everyone gets referred on because of resources (lack of).

In my opinion the best thing to do is for your friend to keep on and on going back to the GP. If they can't get out of the house to the GP surgery, maybe they can keep on making phone appointments. The GP is the gateway to most NHS treatment, and even if it depends on the therapist your friend is already seeing referring them on, the GP can follow it up. I find that a kind of "polite nagging" will often - eventually - get a result!! (Had to do this myself when I needed minor surgery for something). Also we tend to understate problems sometimes but I've realised this is really not the thing to do where healthcare is concerned - it's important to be clear with the GP and other healthcare providers about just how bad the problem is.