what are people talking about
She's introduced as a sulky passive aggressive loner who always listens to music and is upset that her ONE (1) friend isn't with her. And do note, she is explicitly described as a loner. She is touchy about what bothers her and is otherwise quiet/polite.
The only thing that "changed" (more like we just see it now) is that she demonstrates her frustration through violence rather than ONLY sulking. If anything, considering we first saw her being physically aggressive while annoyed when she was with Mako (her one true friend at the time) it makes sense that over time Tomoko would also see her physical violence when irritated. If you're wondering what I'm referring to, it's when she meets Yuu-chan and Mako points out how she's being a passive aggressive cunt like Fang. Yuri punches the wall then.
I would say that people who think the series has retconned anything haven't looked at the old chapters in a long time and are just annoyed by her increased prominence but yes. She has always been a reticent autist. Seriously.