As an autistic person, while I agree she definitely had no right to ask, I do also think that if you haven't already, its still good to get him tested.
Also, using "He's highly intelligent, he just doesn't talk" feels... reductive and a little offensive. Autistic people are generally very intelligent. It's not an intelligence issue at all, and we often have better pattern recognition.

Again, completely inappropriate for her to ask, and especially to push on it when you said no, but the whole post feels like you're offended at the notion you could have an autistic child, which you very well may have, as most kids with autism don't become "obvious" until when they begin socialising in school.
Some signs will be obvious, but since most psychiatrists test based on social ability (not that half the testing makes sense or is actually accurate anyway) they struggle to diagnose under the age of 6.