Personality Disorders's are only supposed to be diagnosed in adolescence, and not in teenagers, since their personalities are still developing.

I would go back to your psychiatrist that diagnosed her, or see another one and get a second opinion, but by what you've written, you've self-diagnosed her.

Maybe she's just a quiet person and prefers to be that way. Maybe she's just normal. Maybe she's just different to you and has her own personality.

You cannot be born with a Personality Disorder, you develop one into your adult years, and it is called a disorder because it disorders your life. If your life is fine and isn't disordered, you probably don't have anything wrong with you.

Maybe she has autism or aspergers.