Brittany does one particularly empowering thing, too: she eventually puts away her scale. Before this, you see her back home in Philly where her insecurities about her appearance resurface. She shed a considerable amount of weight, but she doesn't view herself as worthy of good relationships and the recognition she deserves, and she takes it out on others. This proves that weight loss won't fix your internal demons. Sure, it might help, but it's not a magic cure.
Once Brittany hides her scale, it's clear that she's ready to transition into a life that any well-rounded person trying to live healthier should lead: she exercises because it feels good — and because she has a goal: continuing to train for the next year's marathon. It takes time for her to find a routine that truly works, and she makes smart food choices but doesn't hold back from ordering what she wants. Most importantly, she slowly breaks free from a lot of the self-hatred she had at the beginning of the film and focuses on how her journey makes her feel. And, from the looks of her face at the marathon finish line, she feels like a woman who accomplished a mission and who, despite maybe having more work to do, is happy with herself. She feels like a winner.
