The whole “Mary Margaret’s past” thing actually might make sense now. When Emma told MM that she believed she was innocent and that she believed that Regina was setting her up while MM was in jail, the way MM said “Why would she do that to me?” seemed really odd to me. I had the feeling that they were going to have MM start to remember her FTL life because it didn’t seem like MM and Regina had had any past interactions that would make Regina want to set MM up for murder in her Storybrooke life (she would only want to make her life miserable because of her FTL life). But if they don’t want MM to start to remember her FTL life yet, it would make sense that they might have to come up with some kind of Storybrooke “past” between MM and Regina that would make Regina also hate MM to the extent that she would want to set her up. It doesn’t even have to be a “real” past since time stood still until Emma got there. It could be another “created” memory just like David’s created memories of Kathryn.