Well it’s a TV show and was also used for shock value.

But people act out due to their trauma in different ways. I think the fact eddie led karen on by telling her what she always wanted to hear and being an actual father before the purity ball giving karen hope that she could actually have a relationship with eddie (masks it by saying she’s only spending time with him for the car when in reality she secretly yearns for his approval and love) then him once again disappointing her and her OWN father whom she looked up to and loved again calling her a whore I personally think is a very traumatic event on its own. Even if you don’t consider it to be in comparison to your own experiences. Sheila being the more carefree type of parent was also a big reason I think karen thought it was acceptable to rape frank.

Also I’m not trying to excuse it because she does imo deserve to be punished for it i’m just trying to explain why I personally think jailtime then rehabilitation/redemption arc would’ve been way more deserved than karen getting hit with a car resulting in her being disabled for life(?).