Pretty Little Liars: What Does "A.D." Have to Do With Mary Drake and Dr. Rollins?

We know Mary Drake spent time in Radley Sanitarium, which means we can sort of assume a few things. For one, her roots in Rosewood run deep, so her desire to haunt and harm the liars makes perfect sense. Additionally, it's clear "A.D." must be a little unhinged, especially if they're threatening to kill Hanna in hope of getting answers. We have to say, with her track record, Mary might be a little crazy, too. Coincidence? Maybe not.