We don't get a whole lot of Emily Monroe Norton in this movie. We know that she's the niece of the U.S. President and that she's Charles Kane's wife. Apart from that, you can say that she's a very proper and pretty young woman who deserves a lot better than Charles Kane as a husband.
Her marriage starts out well enough, but over time she gets fed up with how much time and energy her husband spends working at The Inquirer. As she tells Charles,
EMILY: It isn't just the time. It's what you print, attacking the President.
Of course, by "the President," Emily actually means her uncle. She expects Charles to leave members of her family alone in his public criticism, but he'll hear nothing of it.
When Emily finally finds out about Charles' affair with Susan Alexander, she's willing to do whatever it takes to keep the story from going public. She orders Charles to accept Jim Gettys' conditions and drop out of the election for governor, saying,
EMILY: There seems to be only one decision you can make, Charles. I'd say that it'd been made for you.
What she doesn't realize is that Charles is so proud, he'd rather destroy her life than let someone push him around. And in the end, Emily is just one of the many victims of Kane's huge ego.