bio, i respectfully disagree about maggie in mdb. her stakes in the story - she desires to be a ring fighter. she didn't start the story as one, so she didn't have anything to lose except going back to the trailer parks. since the extended family thread was only a light offshoot of the dt, i don't see that as being high enough stakes for such a powerful story. a journey is about regaining what is lost. maggie can't regain what she didn't lose, and can't lose what she didn't have.
frankie on the other hand was created as someone who has something to lose. he's already lost a prize fighter that abandoned and humiliated him; and; he's already lost his daughter. both stakes are high; one is personal, the other is professional. frankie has a journey to make and when maggie walks in the door, she immediately sets him on edge. to me, that's what an antagonist does -- pushes the protag into a corner and then keeps coming; ie, upsets the ordinary world.
frankie's million dollar baby - she's a representation of daughter, fighter, pride, determination and respect all rolled into one package. exactly what frankie is missing but a flaw he doesn't recognize until his ordinary world changes. when frankie pulls the plug on her assisted life machine, he's both physically and symbolically letting go of his flaw and recognizing that he can go on as a healed individual. the film is his story and what this scrappy, determined girl did to change his life.
anyway, that's how i see mdb. everyone has a different perception and half the fun of writing lies in the interpretation.