Through the scenes, we see Maggie grow as a person and as a boxer, we observe not just only the "physical" side of Maggie, but also her mental character. When she first meets Frankie it is obvious although she was composed and determined, she did not have the skills to be a boxer but she did not give up she kept at it and eventually she became the amazing boxer "Mo Cushle".
Alot of film techniques are used to show Maggie's development as a character, among those are Montage, "silence", voice-over, close-up, two shot, the use of darkness and much more.
Some techniques such as the "silence" can maximize the feeling of isolation and can create immediate and very effective "tension" within the scene. While using silence can create an effect of isolation and tension, using Montage is a great way to show progress, through the scenes of Maggie's development we see alot of this effect either fading quickly from one to another or fading slowly.
There are two major changes to Maggie in the Million Dollar Baby. The first is when she is finally accepted by Frankie, this change is one that Frankie helps her with, her change from her old life as a waitress into a world class boxer. The other change i believe is when Maggie is crippled and in bed. When her family comes to scam money off her she finally sees the bad side of her family, and that they are truly heartless and couldn't and wouldn't careless about what happened and what would happen to her. I believe when this happens she makes up her mind about her future.