June represents everything Connie despises. June is responsible; Connie is careless. Connie notices the dishes that were left in the sink and thinks that maybe she was supposed to wash them. June would have washed them without giving it a thought. June wears a dress and high heels to a barbeque and socializes with her parents and relatives. Connie dresses to attract boys at the local hangout spot. June serves "as the standard to which Connie's own behavior is always compared and found wanting. Connie believes she is better than her sister because she is more beautiful."
I don't think Oates meant to say that Connie's behavior and manner of dress caused what happened to her. Connie is just a typical teenager, and the differences between her and June show just how typical Connie is. What ends up happening to her could happen to any girl.