You're feeling that way because the letter makes it clear she's your therapist, not your mother or a friend or whoever we may prefer they be. She wrote the letter clearly from the perspective of a therapist (and a good one) which is good... but it still sucks in comparison to what you might want her to be for you.

I get it. I hate that my therapist is my therapist. He would be a great family member, spouse preferably, or even friend. Are real people ever so nice? Not in my life. I'm feeling very depressed because of it.