Both of my children have been diagnosed with ASD (would have been Asperger's before that was removed from the DSM). Let me echo what AnnieQuill said - it's not a bad thing, and it's not a new thing. It's an aspect of her personality, but she is the same kid you know and love.
That said, have you looked generally at information about Asperger's Syndrome, or have you looked specifically for information about how AS presents in girls? There is a fair amount of evidence at this point that its presentation in girls is not that same, and its incidence in girls may be higher than previously believed because of the differences in presentation.
Does your DD have any sensory issues? DD12's school counselor referred to the "unholy triad" of ADHD, anxiety, and sensory processing disorder as being characteristic of undiagnosed autism. If she has all three, I'd consider asking an autism specialist to rule it in or out for you. It's better to know, even if you dread the answer.
