To avoid this ending, you have ignore your mom's request to help the girl and instead snoop on your brother as he dicks around on his phone.
You see him enter a PIN to unlock the device. That code also works on his laptop, which contains a file in which he bitches about his dad putting all his stuff in a box on the veranda. Among that stuff is a metallic dog head, which you're supposed to place on the locked door leading to the backyard, letting you open it. Now that we type it out, it all seems so logical and obvious.
Note that the game won't even let you search the box unless you've previously invaded your brother's privacy. So the correct way to play this game is: 1) Try to escape through the garage and lose, 2) realize you need to go through the back door and spend hours searching for a nonexistent key, and 3) give up, turn Zoe into an unfeeling, voyeuristic asshole, and stumble upon the correct solution. All so you can get the "good" ending ... which leads to Zoe getting straded and rescued months later in the main game by her MMA uncle who suplexes zombies and wrestles gators. Totally worth it.