The Therapist-Patient Privilege
This breaks down the exceptions of what information is privileged with a therapist.
I don’t believe being trans* falls under any of those categories. While it may vary by state, your information is between you and your therapist unless there is a law being broken or someone is endangered. As long as you don’t sue your therapist for malpractice, you should be fine.
Here’s another link that is intended as a Q&A for therapists, but it’s basically saying that minors have the same confidentiality unless a law is being broken, from what I can glean.
Submitted by nameoffives
Something of interest.