It is possible that some of those decorations may not come back up after the holidays. Some of the 60th décor (Main Street banners and such) came down for Halloween Time, and it will probably stay down for the holidays. I don't know for sure that those will pop back up in January, and I don't know how much more -- if anything -- will be taken down for the holidays. They may or may not come back. The decorations are probably not as thorough and extensive as she may think, but I'm pretty sure the Castle will stay as it is now for a while (Diamond Anniversary décor).
The holiday season officially ends on January 6th, but It's a Small World Holiday will probably be open until late January (and there are holiday decorations around that immediate area while it's running).