I take it you mean Asperger's syndrome.
First of all, a clear and complete diagnosis by a psychiatrist is essential. Only then can you proceed safely with the issue.
In general terms, it is much better for the sufferer to be aware of what is wrong with them. If they are not told and supported, they continue to be anxious about what is happening to them and also about what might happen to them in future.
For m ost people, it helps them to kn ow about their illness, what they might expect and what help they might get. That in itself greatly reduces the natural anxiety
which is present in these situations.
That said, in a few, rare cases, there may be good psychological reasons for witholding dignostic/prognostic information at this stage, and that is a decision best left to the assesing psychiatrist.
Realistically, this person is going to find out sooner or later, and in my view, it is much better now rather than later. After all she will have a right to know her diagnosis.
In addition, with this condition it is important that appropriate treatment and support is made available as early as possible.
What is critically important is that her family educate themselves as much as possible about the condition and about what they might do to help.
The mother should be encouraged to visit the website here
which in itself is very informative, but which also provides extensive links to other resources and support systems.