Most people keep their past secret for a reason, mostly if they did do something bad or something bad happened to them. I honestly don't think revealing any skeletons in Frankie's closet would reflect negatively on who she is or her character in general.
Besides, the past is the past, it's apart of who we are and as we saw with Wilt, it's something we have to accept and simply can't run away from. I also think that if by chance Frankie did do something horrible in the past, odds are she would be harder on herself then anyone else to her.
Mac and Eduardo and the others would never hold anything she did against Frankie personally.....Bloo is another story, but he'd more then likely make fun of her or laugh or something. In anycase, I know the Foster's gang would accept Frankie back no matter what she's done IF she's done anything at all.
I also think that if they do make a movie for Frankie like for Wilt they should NOT have her travel across the country to find her parents or whatever. As much as I would love to see Frankie in the lime light, I don't wanna see the exact same set up used with just a different character being focused on.
I think the way Wilt's movie worked out for him was just fine, and if Frankie deserves a movie (which she totally, totally, TOTALLY does considering all the work she never gets appreciated for
) she should get one that's unique and different from Wilt's.
Btw Home fan, that's one of the BIGGEST mysteries behind Frankie: her family. We don't know jack about her parents, if she has any siblings etc.