Cora I think because she was new in town and didn't already know Jack, it gave her a different perspective.
Rebekah Yes, me too. I wish she had put in something that fleshed this out a bit more. Like learning that someone close to her had been in an abusive controlling relationship or something. Although that whole scene in the restaurant at lunch would have raised a lot of red flags for most people. i think that's when she knows something is wrong. Very wrong.