She is a free person so she have all right to talk about this and any subject. And also she is free to not talk about something if she doesn't want (sure she can be challenged on not talking when it is a topic she usually talks about).
But we are also free to agree or disagree with her, but don't need to witchhunt or the like.
Absolutely, everyone should have the right to talk about any topic.
I think the problem happens when famous people come out about topics for which actual professionals have deepened opinions on the matter, so the problem is that a famous person leverages their fame to push their opinion and that is where it's lousy.
It would be much better to hear someone who is famous for their life's work on gender identity than to hear the writer of a children's fiction novel. Her opinion is probably just as good as ours.