Yeah I ask this, because I just don't really understand or know.
Brony sounds pretty un-logical, because there's a word: "Bro" but it could be changed to normal name of MLP-FiM fans otherwise. Because it sounds so much used name, so it may be best to call them too as brony.
Pegasister is the term that I have seen very rarely used. It could be more logical, because it has word "sister." Not sure though.
By both I mean that Pegasister and Brony both fits for girls/women.
Idk really about you all. What is yours opinions and what do you all say? I am just curious and I don't really have opinion if they are called as bronies. But wouldn't that be a little too un-logic?