By Jan 6, most, if not all, of the decorations in the theme parks should be down. Jan 7 is the half marathon and Jan 8 is the full marathon. We've done them the past two years and the parks were about Christmas-free by then. The resorts may still have them up a few days later. The WL decorations came down Sunday night/Monday morning during the night while we slept on Marathon Sunday two years ago.
So if she arrives on Jan 2, she should still be able to see some. Most of the shows/parades will be over, though.