IMO, the character of Mary Sunshine in CHICAGO accomplishes the following:
1) Demonstrates how the media interacts with the legal system to get "hot" (not necessarily "true") stories for public
2) Characterizes the 'sob sister' Newspaper Reporter that first appeared in the 1920s
3) Demonstrates that in the 1920s, women were finally being taken seriously enough to do a "man's job." (newspaper reporter)
Those of you who haven't seen production may not fully understand 3rd point. :)
"I say YOU'RE the CUTEST one. No, I say YOU'RE the CUTEST One. And we go on like that from dawn to three."