Character Analysis
This lady's had it up to here with Jane and Michael, despite how likeable they are. An uptight and evidently incompetent nanny, she abandons the Banks family at their hour of need, when Jane and Michael run off. Katie Nanna announces her departure to Mrs. Banks (once she can get her attention) and huffs out of the house. Lame.
Even though Katie Nanna is a lousy, bargain-bin nanny who can't tell the difference between chasing after a kite and running away from home, she does one important thing: she provides the inciting incident for the whole movie. If Katie Nanna doesn't quit her job, then there's no reason to hire Mary Poppins. No Poppins, no movie.