I would be wary of a psychiatrist ready to diagnose so quickly, especially in anyone under 18 (I am guessing here), and prescribe her meds. I am not saying she isn't right, it would just make think that a second opinion from another psychiatrist might be helpful since this one doesn't think speaking with your daughter's therapist would be helpful or necessary, especially after a varying diagnosis...it seems very odd!
And kudos to you as parent for being so careful and attentive.