In both Up and Toy Story 3, a postcard can be found addressed from Emma Jean to Carl and Ellie. For a long time, the identity of Emma Jean remained a mystery. Recently, however, the director of Up himself, Pete Docter, sat down for an interview with Jonathan Carlin and told her story.
Emma Jean was something of a love interest for Carl before Ellie. There was of course some tension for a time between the two, but they eventually smoothed things out and became very close. The two often did activities such as shop together, and at some point Emma sent the postcard that can be seen in Carl's house and pinned to Andy's bulletin board in Toy Story 3. While the mystery of Emma Jean has been solved, it is still unknown how the postcard ended up in Andy's possession.