MMLTW, CvilleMother & klily444: : IMO, the combination of your individual theories/insights provides what I believe to be the exact circumstances that caused Hannah to become lost and take the route that she took.
A brief synthesis of MMLTW, CvilleMother & klily444's posts:
After finding herself lost and wandering for a bit, Hannah resorts to using her phone's GPS to lead her back to the area of her apartment/the parties. The central intersection near that area is 14th and Main.
However, when Main Street crosses 14th, the name of Main Street changes to University Avenue. Unaware of this easily overlooked technicality, Hannah inputs "14th and Main" into her phone's GPS.
Since, technically, the intersection of 14th and Main does not exist, Google Maps defaults to "4th and Main." (If you input 14th and Main yourself, you will find that it indeed defaults to 4th and Main).
Assuming that Hannah was close to Grady Avenue when she input 14th and Main into her phone, the exact route Hannah took that night is the route that her GPS would have provided.
***All credit for these ideas and theories goes to MMLTW, CvilleMother & klily444. I contributed nothing. I merely summarized their posts into a short, cohesive story. I would have quoted each of their posts here but could not figure out how to do so.***