She's already been getting the same treatment from MC for years. They do the same shit to each other and always have. From his perspective, she's always a bitch. From her perspective, he's always an asshole. But they both highlight the fiasco we saw in the flashback as the moment they became truly vicious.
When we get to jump into their story, there's now people like Ashley and Emily influencing both of them to not be so hateful. It's more about getting both of them to recognize they're both to blame (yes, MC is innocent in the Emelio/Nathan ordeal, but that's all) and to start healing from there.
I understand some people want to remain vindictive to Kayla, but I don't think that's what the story is supposed to be about. We can save that hated for someone who truly deserves it... *ahem*... Sierra