In another fan theory, someone suggested that Karen Minty may have discovered what Joe is capable of, which explains how she reacted when he broke up with her. She was too afraid to do it herself, so when he did it she remained calm and saw this as an easy way out.
It also explains Karen’s weird warning to Beck about Joe in reference to Candace. Karen heard Joe saying her name in his sleep, which could’ve prompted her to look into Candace. She could’ve figured out the same theories as Candace’s friends – that she’s dead and Joe had something to do with it. She tells Beck, "Maybe he'll do [to you] whatever the hell he did to Candace."
Either way, Karen didn’t want to get involved in case he hurt her too, so she tried her best to warn Beck. After all, we didn’t see her again after the break up, despite her caring and invested relationship with Claudia and Paco. Karen definitely didn't want to hang around for too long.