Here’s the thing, she made three attempts to kill Kelsey herself. Clearly, she wasn’t fully committed to doing so.
She was willing to drive that incredible distance, which shows that she atleast entertained the thought.
By these actions, she demonstrated that she was comfortable with Kelsey being killed, and the fact she didn’t stop this damn thing, is further evidence of that.
She just didn’t want to do it herself.
That’s why I don’t think it’s a stretch to believe that she was willing to clean, because it was better than the alternative.
He was able to talk to her like that, and she was receptive to it, because she was in on it.
She wanted it.
And that’s why she’s so terrible.