It may be that she is autistic, it may be that she is simply internalising emotions because it is not safe for her to share emotions with her parents. This can sometimes present in autistic-like ways. I think the important thing is a) she doesn't self diagnose and b) it doesn't become her entire identity, whether forced or unforced by internal/external pressures.

It may be that she needs help with processing written words and would benefit from counselling. In that she'd be like a significant amount of other young people - and this doesn't mean 'neurodivergence' it simply means acknowledge her individuality and provide the help she requires.