It's her new Christmas song! It's going to be an original song too since there were a few people who tweeted a couple months or so ago that they were writing new Christmas songs for her.
I love that she's doing a Christmas album though. She needs to get her fanbase back and a Christmas album will be perfect for that in the UK.
And if this does well, they need to get a new album out by Spring. Apparently she's been working on the Xmas album and her next studio album at the same time. I guess this is the kind of stuff that happens when you finally have good management.