If you were to pinpoint an event in Ogiue’s life that began her path of self-acceptance, you would not be incorrect in saying that the catalyst was her arrival in Genshiken. The story makes that much clear. However, what I would like to remind people about, even if no one’s arguing for or against it, is that the signs are clear that Ogiue changed because she had a deeper desire to change. If she were truly resistant to the idea of changing herself, it would not have happened.
While Ogiue’s preference for clothes changed throughout the series, in the very same conversation where Saki convinces her to start wearing better clothes you learn that Ogiue had already undergone a small makeover in the transition from high school to college. Her signature paintbrush hairstyle was something new, and she switched out her eyeglasses for contacts. The message is, “I don’t want to be the person I was,” though it’s marred by the fact that she isn’t sure at first what person she wants to be. Does she want to be more of an otaku or less?
This also comes out in her apparent interactions with the school’s Manga Society, where she antagonized the girls in the club. It’s clear looking back that all she really wanted was friends, but she projected her own shame onto them. Still, as poor a reaction as she had towards them, this was also a sign of change.
There’s that saying, “help comes to those who help themselves.” In this case, I think it happened on a subconscious level.