Quite simply, she becomes a stronger woman. While before she tolerated everything from everyone, by the end of the story she doesn't. The big climax of this is during the dinner, when she tells everyone (her husband, his kids) off for how they treated her, and she leaves with Shug. While before she felt weak, like she had to put up with everyone, by the end of the story she develops self esteem enough to stand up for herself. She becomes empowered and accepts her life for how it is. She also experiences love (with Shug) and a sense of family with those around her (like...I don't remember the character's name but in the movie Oprah played her). Part of her empowerment is due to the fact that she found out her sister was alive, and when Celie finds out her sister is alive, she sort of comes back to life herself after so many years of "death" through silence and depression (even though, as she says, at least the dead get to rest while she had to work).