Hey, Kura!
What we need is for your co-author to email us with permission for you to post the story on your account. If they have an AFF account, their pen name would be good. If not, we'll need their email address for our records. We never publish that information, but we do need to have it.
FYI, the only reason I'm not participating is that I'm already working on a Christmas story (which doesn't qualify because it's not a one-shot) that I probably won't finish by Christmas. But all the best in your holiday-themed endeavors!