I mean, I don't think Elizabeth ever claims to be completely different from all other women. She's saying that in this one specific area she was different from many of the women of Darcy's acquaintance. She has reason to think that women have treated him this way because she watched Miss Bingley do exactly that. And of course, he was indifferent to Miss Bingley, despite her being attractive and intelligent and his best friend's sister. Really, Elizabeth's point is not really even about herself. She's making a point about Darcy, that despite his apparent pride, he actually didn't like to be flattered all the time. He chose the woman who didn't flatter him over the women who did, because he actually does value sincerity and like to be challenged--that's the point.