I doubt that many people hate Brienne as a character, they just hate her as a POV character because they find her chapters unbearably boring. So it's less "I hate Brienne because she did this or that" than "GODS NO I DON'T WANT TO READ ANOTHER THIRTY PAGES OF NOTHING HAPPENING!" ;) So in this case I think it's less people hating a female character than people just disagreeing on which chapters are interesting and which aren't.