I think that statement is a really really unhelpful statement. And she contradicts herself - on one hand saying 'you're happy' and then on the other hand saying 'you've not made a commitment to being happy' which automatically implies that you're not happy.
Maybe the problem is in defining the term. What does she mean by using the word happy? All of us have passing moods. They come and go. Can we snag one moment and define our lives by that? Is happiness only that feeling where we feel exhilarated or can can happiness mean just a sense of well being that is the prominent feeling.
But if you're hurting and you've sunk into a depression that doesn't pass, how can your T have the gall to say you're happy but don't know it. That kinda pisses me off. It doesn't validate what you're going through and the suffering you're experiencing now.
"So, T, why don't you dump another concern on my head? It's not like I'm not feeling terrible already, now I have to wonder if it's true that I feel terrible"

(sarcasm here)