another theory as why Cece and Ali dressed the same that night, maybe they indeed lured Bethany there and since she's unstable, they wanted to make a bad joke on her, let Bethany believe she's seeing double(maybe this is were the twins theory is done) and make her believe she's crazy but not kill her or hurt her physically. Bethany, as unstable as she is, took a rock and hit Ali, then Cece hit Bethany. Cece dig the grave but is interrupted by Melissa.

God, you guys are awesome! I LOVE this! And this totally seem like something Alison and Cece would do!

Besides, Mona found evidence that proved Alison lured Bethany to Rosewood, so your theory would totally fit on that!

If you have any other theories, send them to me, because this one is awesome!