Return to Sender
When Quentin is searching for Margo Roth Spiegelman, he thinks that she is leading him to one of the many pseudovisions that are more numerous in Florida than sinkholes. These pseudovisions are similar to the paper towns, "subdivision[s] abandoned before [they] could be completed" (2.8.21). In other words, they're places that aren't really places.
However, it turns out that these are the wrong sort of paper towns. The pseudovisions are a red herring, a clue that isn't really a clue. Margo isn't leading Quentin to them on purpose—but maybe she would if she recognized that she is a pseudovision, too.
Her paper girl speech (see "What's Up with the Ending?") that likens herself to a two-dimensional paper girl makes her seem like a pseudovision, too. She abandons her home before she can be completed, creates a sense of herself for others that isn't really there beneath her surface.
The difference between the pseudovisions and Margo Roth Spiegelman is that Margo Roth Spiegelman wants to be completed. If she stayed in Florida, she, like the pseudovisions, would never be completed. Florida is where things go to die, not to live, and Margo Roth Spiegelman isn't about to let that happen to herself, so off she goes.