As she gets swept up in the events surrounding her crime, she learns to scheme, manipulate, lie, cheat, and steal.
She becomes a tiger, scratching and clawing her way to the top (well, the top as she sees it, anyway) she becomes Velma, stealing from Velma not only Mamas attentions, her lawyer, her trial date, and her rhinestone shoes, but also her ruthlessness, her celebrity and her ambition.
Amos is an average guy, not very good looking, not very smart.
Roxie says about him that whole is a whole lot greater than the sum of his parts.
Interestingly, in the film Roxie Hart, the screenwriter Nunnally Johnson went to great lengths to make sure we understood that Roxie didnt actually kill Fred Casely (Amos did), and Johnson added in some idiotic tap dancing and a handsome young love interest for Roxie to end up with.
The movie and Roxie lost all the grit and edgy humor of the original. Amos is the only character in Chicago whose motives are entirely pure, never selfish.
Unfortunately, by that time, her ambition has outpaced her love for Amos.
But we see Roxie's real feelings for Amos in Roxie she does care about him (you could love a guy like that). She obviously isn't attracted to him, but is she in love with him? After years of dating bootleggers and gangsters, Amos was safe and sweet, but for a girl like Roxie, who dreams of fame and fortune, safe and sweet only last so long.
For the first time, she can step back from the circus and see it for what it really is.
And in a way, she returns to her original world view.
She operates exactly like a child of five or six, perceiving the world only as to how it affects her.
Every move is selfish, every idea foolish and ill-considered, and yet she remains strangely sympathetic because we know her selfishness is not malicious; its childish. Chicago is largely absent any kind of genuine emotion.