Glad to read I'm not the only one who thinks so. I have a very low tolerance for Arndt and no sympathy whatsoever. And yes, she thought JDI; at least initially. Or anyway, that's what she later said that she thought.
She's a drama queen. IMO, it was much easier and more effective for her to deflect. She was the one who lost control of the crime scene that morning, sent JR on a search, and after he brought JB up from the basement she moved the body again, and then allowed JR to further contaminate it with a blanket. And then she blamed everyone else at BPD. She faxed a list of questions to Team Ramsey, exposing important evidence. She befriended Patsy in secret. In the end, she sued BPD saying she "felt a lack of support" - and lost.