Judging by your username i'd guess you're ... 18? When I was that age, I'd be out drinking 5 nights a week, sleeping around with anything and everything and generally having a 'good' time (or so I thought!). I didnt know what I wanted to do/be and wasted a lot of my time/energy/money needlessly having fun and waking up feeling like crap, both through drink and shame.
Now, you seem like a nice intelligent girl so you probably don't do craaazaay like I did, but maybe your therapist assumes you do. Or she might suppose this is just a 'phase' you're going through (as most teenagers have), so thats qhy she might question you're maturity.
Next time you meet with her, show her that you are mature, that you are ready for hormones. Ask her why she feels this way, and what you can do to make her convince her otherwise.
X