Blossom Cooper first appeared as part of a gaming-nerd trio at Griswald's Grammar School with Tuan Hoang and Mosstyn Corkindale (Corky). She appeared to be the dominant personality of the group, ordering the others around. She was distrustful of Shauna Wickle when she sought assistance from the group when her friends (along with most of the rest of the school) were hypnotized by Lem, who turned out ot be an alien onion creature, believing (correctly) that Shauna would return to her own friends when they were no longer hypnotized, and not hang out with the "nerd group". In a way, this was self-fulfilling, since Blossom pressured her friends into not continuing to fraternize with Shauna. Of course, by that time Blossom had already betrayed Shauna by (along with Tuan) attempting to get Lem to hypnotize her instead of helping her stop him, because Blossom preferred the atmosphere of the school when most of the other students who normally tease her were hypnotized.
A few years later, Blossom would fight another girl, Tania Lewis, to become Top Bitch of the Year at the school. Following this, her talking-back to Mr. Knott, known for his stern discipline, resulted in Mr. Knott's collapse and retirement, leading to Ward Bostwick taking over as the new head disciplinarian with a "new-agey" approach.
Shauna recently made it her mission to get Blossom back on the side of good by befriending her. For a while it seemed to be working (though Shauna's other friends never particularly warmed up to Blossom), but it backfired when Shauna's brother Darren rejected her romantic overtures and she retaliated by revealing a secret Shauna had told her, that Shauna was responsible for Darren's imprisonment. He then left in a rage and trashed Shauna's room, and Shauna broke off her friendship (literally breaking the friendship bracelet). However, Shauna still later referred to Blossom as her friend, and got into a fight (and possibly ended her friendship with Charlotte) on her behalf.
During all this other drama, Blossom and Linton kissed, soon after Linton had some romantic difficulties with Claire, but Blossom later indicated a lack of interest in pursuing any romantic connection with him (and he was showing signs of being scared of continuing any relationship with Blossom anyway). (This stuff gets very soap-opera-ish sometimes.)