In my experience with friends family and myself, the hardest important thing for people who are autistic is learning how to function in society. If it's so bad that she can't adapt or adjust, she *can* get disability as an adult. I have an ASD, and my experience definitely does not speak for autism in general because it's not a disabling form, but functioning in society and trauma from how people who were unaware of my condition treated me as I grew up are my biggest problems.
High functioning autism can be extremely case specific, so take most non-professional advice with a grain of salt, but remember that autism doesn't have to be a stigma, and that being diagnosed with autism doesn't instantly make every symptom appear in a form which the person can't work around or cope with, especially in intelligent people. I'm also gonna say that I agree with sonnyjaboy, and if there's any trouble with her in terms of communicating with people, *DO NOT* turn a blind eye to that, because the more accurately and eloquently she can speak for herself when she needs to, the much much easier life with autism is going to be.