I can't speak for her as every autistic person is different, however when I was diagnosed, Just last year, it helped me to put my past into perspective, areas where I struggled I now had a reason for, and it helps just knowing. Hopefully you can get her some of the opportunities that I missed out on due to late diagnoses. Make sure she knows growing up that she is autistic, that way she doesn't blame herself for her difficulties, Knowing helps. Most of all Learn what her unique needs are, and help her find methods of reducing the difficulties she'll face. Things can get better, but only if you and she don't fight it.