I agree with WePow.. Would have been better to let t know beforehand that your friend would not be alone for her appointment, but that's great that you were able to step up for her also.
I have kind of a different opinion about it when it comes to myself though. I'm currently helping a friend who is in therapy right now but would not go in one of her session even if she asked me (unless I think her t is unethical or something like that) because I would be afraid to enable her with her communication problem and disempower her (like if, by speaking for her, I was telling her: "you're right, you cannot do it, I'll do it for you" . She needs to learn to step up for herself and therapy is the best place to do it in my opinion. BUT this is the reaction I have with my friend and the situation is probably really different from yours (depression is not one of the issues my friend has).