Somewhat surprising ending If you look at both both girls' stories at the beginning, it seems like Megan had the best chance to fit back into society. Although she had a history of running away, her crime was not extremely violent (from what little we're told). She's energetic, driven, charismatic, fairly focused, aware of her family's faults, and could easily become a hairdresser or stylist which was her hobby while locked up. She's also beautiful and stylish which can make a difference when getting into that profession (and of course that's why she's on the DVD cover).
Shanae on the other hand seems unfocused and passive. She seems to have accepted her situation and is making the best of it. Her mother dies suddenly right when she's making great progress. And there's one fact that this movie glosses over repeatedly: she's a murderer. She stabbed a girl three times which killed her. While Shanae is going to the prom and enjoying teenage life, there's another girl in a coffin who will never experience that. If this ever occurs to Shanae, she never speaks about it.
The surprise: Shanae is the success story. She gets good grades, never gets into trouble again and has a lot of people proud of her. She even becomes more articulate, able to express complex ideas that the old Shanae probably couldn't have formulated. The director commentary said she's only had more success after the documentary finished. Despite being a murderer and losing her mother, she's everything we could hope for.
Megan on the other hand goes out of control. Her family only exists for her to yell at and blame her problems on which we get to see over and over. Her real family is her loser friends she hangs out with, whoever they may be on any given day. Her only apparent goal is to follow in her mother's footsteps, straight into jail. Her street "Bawlmore" accent becomes thicker and stupider and shows which direction he's headed. In the end the director asks her if she could have three wishes come true, what would they be. Megan, clearly under the influence of something, can't think of a single wish worth asking for. She's perfectly content at that moment and that's all she cares about.
If you watch it again with the knowledge of how things turned out, then you can see what was really going on. Shanae was quiet but that only hid her inner drive and confidence that we didn't know existed. Megan was a drama queen, faking sickness, seeking attention from everyone, breaking rules, and constantly manipulating the staff to get what she wanted. What looked like drive and energy would actually become weaknesses in the real world. Shanae returned to a family who cared about her and was proud of her. Megan went back to a surrogate family of clueless corner kids, a mother she has no respect for, and no one who really cared about her.
I wish they had given more information on the girls' lives before they were incarcerated from other more objective people. We know next to nothing about the crimes they committed. This made me feel like the director purposely downplayed these clues and withheld information in order to make the ending more surprising which isn't fair to the audience. All we hear are bits and pieces from the girls themselves and very brief titles saying what happened. For example Megan's habit of running away from foster homes was actually a strong clue of how her brain worked than was implied when she was released.