Athena made a point of trying to be Sugar's friend when most would just use her or trash her. It was just a double-edge pang of pity, not just for the girl's unenviable situation but also because Athena (and only Athena) remembered exactly who this caricature of an airhead actually was. Before she was transformed, Sugar used to be the geek Kyla Leeson.
Kyla was quite possibly the smartest girl in school, but being a geek kind of made her somewhat of a social outcast. Oh sure, she had geek and nerd friends, but she was always looked down upon by the "popular" crowd, especially since she wasn't really all that attractive like they were.
So, obviously, Athena pitied her. The most intelligent girl in school had become the dumbest and sluttiest girl in school.
But Athena was the only one that noticed.