I'm sorry to hear about your situation, and I hope and pray that you and your family have a safe and enjoyable trip. It probably would be a good idea to get a wheelchair (or motorized scooter) for her, I don't know if you are planning to stay onsite or not, but I think there are several scooter companies that service WDW. We used ScooterBug once and had a good experience. You can rent one for the length of your stay. You can get them at the parks, but at times the walks even to the rental locations can be taxing for some, and the busses can handle the wheelchairs or ECVs. I would also let Disney know your situation, as they may be able to help you in terms of addressing all your sisters needs. Since you specifically mentioned Christmas, and though it is sadly not there anymore, showing her videos of the Osborne Spectacle of Lights might help her while she's still at home. It really is a beautiful display, and WDWMagic even has videos of it on youtube. Those videos on youtube, though for many they feel it spoils the experience, due to your situation it might help make the time between now and your trip more enjoyable. It may also allow her to experience things that she physically might not get to enjoy. Some don't want to be spoiled, but if it puts a smile on her face or makes her more optomisitic, then I'd do it. Even if you just do the videos of things that are no longer there, like Osborne or Wishes (Or Christmas Wishes).
Sometimes people get so locked into doing everything, or being moths attracted to a bright light, that they walk right by things that can be enjoyable, like visiting the resorts, as those are much more laid back, and some have cool sights like Animal Kingdom Lodge, and the animals. Also tking into account that you might be spending a lot of time at the resort you are staying at, so picking one that would be most beneficial might be a good idea. Another option might be something like the Keys to the Kingdom tour, as it's very informative, and you get to see some neat stuff, while also having a Disney guide with you in case there are any emergencys and they do allow wheelchairs. Reading about Disney might help, as that is a very happy place to read about, and it can help you when you visit, as you can learn nuggets about the various attractions and locales that make them all the more enjoyable, like the Nixon-Contemporary connection, or the Beatles and the Polynesian. I do think though taking into account her direct likes and tastes would be a good idea, even if that includes going to places she doesn't even know about at Disney World, so she gets to experience it. Though the parks are great, many often find the thing they enjoy most at Disney is someplace else on property as it falls more in their wheel house. I do hope you and your family have as much fun and safety as possible and that you all have fun, and she smiles.
I hope you all have a great time!!
