She could have escaped through the front or back door. What if they had a wall around the backyard? What if she knew that Gray could easily outrun her? Maybe she was thinking I can't get away on foot but there is no way he could keep up with a car. Then when in the stress of escaping the bedroom she left the keys behind she took the gun out of the car and was trying to get to a door to leave when he found her in the kitchen and she was trapped again. If she had gone back into the garage and tried to open the garage door she would have had to wait around 30-45 seconds for the door to open. A lot can happen in that time frame.