Any therapist/counselor can diagnose, the diagnosis is for the therapist, to help them help you. If you want to know what you're being treated "for" just ask your counselor and discuss it with her. There's no such thing as a "true" diagnosis as it depends on who/why/what the person diagnosing you is "doing" with the diagnosis.

Obviously you have an anxiety problem; why do you care if it's panic attacks or GAD? Work as best you can on it with your counselor and take the Xanax as needed. Your counselor might be more interested in your "obsession" with wanting a diagnosis. What would having one mean to you?