I agree with most of the other posters, Ginny is judgemental, and probably rather possessive too. Even during the battle she's unwilling to let the (obviously capable) Cho take Harry to the Ravenclaw common room. I can certainly see Ginny making digs about Cho, more than Harry would about Michael or Dean.
I've always assumed that she's good looking, because it's other people, not Harry, who say that she is, but she's not prefect material, and she's probably proud of that fact. She's less likely to ignore general insults than Harry. (The Smith incident, which Harry was prepared to ignore, she wasn't).