Chlöe is introduced in season two as Bryce's new girlfriend. Although she initially tries to intimidate Jess out of testifying against her boyfriend in court, she comes to realise that Bryce really is a monster (and raped her, too, when she was unconscious in the clubhouse). Despite that, she gets back together with him, and while attending the Spring Fling she reveals to Jessica that she's pregnant with Bryce's child.
Much of Chlöe's season three arc revolves around her blossoming friendship with Zach and how she leans on him during her decision to get an abortion and finally break up with Bryce. After she goes through with terminating the pregnancy, she later tells her ex-boyfriend about it, and at first he seems relatively understanding. But of course this is Bryce we're talking about — he doesn't truly care about women, even Chlöe. The thing that really upsets him about the situation is that she's become close to Zach, a factor that eventually contributes to how Bryce dies. But no, Chlöe isn't the one to do it.