It's common for female fans to dislike the term "pegasister," so many refer to themselves as bronies. I'm fine with girls calling themselves bronies. After all, "pegasister" is such a lame term.
Don't quote me on this, but I think the "Brony Census," as of around 2015, found about a quarter of older fans are women or teenage girls. That percentage was said to have risen quite a bit from earlier years.
Amusingly, almost everyone I've seen in public with an mlp shirt has been a little girl (and one 30+ yr old woman with a 1st gen. shirt). The most amusing was probably the teenage girl who looked as though she was wearing a Pinkie Pie scalp on her head I have seen a small number of male bronies in public, for the record.
I'm under the impression, from what I've noticed, that a higher percentage of the artists and fanfic writers are women than the brony population. In general, not just with mlp, most fanfic writers are women (and possibly most artists too?)