In other zombie circumstances, maybe I wouldn't. However, like you said, there's a slight chance of saving her. And even if I didn't close the door right behind her, the zombies would probably focus on her that moment in time and I would still have a chance to escape out the back garden or something. The more I think about it, the more I think I probably shouldn't have tried saving her :), but hey, in those situations you listen to your guts and you have to make the decision in an instant.
I guess me being a girl, it would have helped if the damsel in distress was a strong man rather than a female teenager...However, in any circumstance, you know what they say:
"If you want to walk fast, walk alone; but if you want to walk far, walk together"
If I was on my own I'd try to help, but If I had people close to me with me, then I'd close the door because they're more important to me. (sorry running girl!) If there ever Is a zombie apocalypse I'll probably be one of the first ones to day, so I don't have to worry about these decisions!