I would have to check the rulebook to verify, but it requires more than just an action if I remember correctly. Moving into a zone with zombies in it stops your character's movement. Your character would then have to use further actions to move from that square. If there is one zombie in the zone, you would have to use three actions total to make it through the zone. The first action would be your initial move, and actions two and three would be used to escape the zone. Now, when escaping the zone, you would get to move her full two spaces.