She knew it was the brother all along. Read this bit.
According to court papers the woman told Jared: " When did you think I was going to find out? When I realized you didn't have a tattoo? When we didn't use Joe's car to drive home? Or when you didn't know how to get to my house because you've never been there?' "
So when she turned up at the house, she knew her boyfriends car wasn't there, so he couldn't be. the dirty little mare.