It's a personality disorder, so normally people are only diagnosed when they are adults. I think you can get a dx when you are 16 in some places though, I can't quite remember.
Usually they do this because children's personalities are constantly developing, and there are also teenage hormones and the like that you have to account for. So for personality disorders, doctors usually reserve judgement until the personality is a bit more stable, so to speak. If you have any concerns about her behaviour though, there is no harm in talking to a doctor about it and seeing what sort of services are available.
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Said the apple to the orange,
"Oh, I wanted you to come
Close to me and
Kiss me to the core."
Think you're ASD? Get thee to a professional!