I don't see her as Stacy Morasco evil either, but I think she is extremely passive aggressive and has been motivated subconsciously this whole time by her feelings for Dante. She may not have sat down and planned it all out, but she still positioned herself as Dante's confidant vs. lying Lulu, and she still made sure she was right there ready and willing when Dante was at his lowest point, AND she still makes sure to get in her little "but Lulu lied first!" digs whenever she gets a chance. (Btw, I don't mean to make it sound like I blame Valerie more than Dante - he's the one who cheated on his wife.)
Right, and also I feel like half her scenes the past few months were talking to someone about the ONS at the police station, like I'm not sure how she thought people weren't going to find out eventually.