First, I'm glad you're letting yourself have your feelings about changing the date. As a counselor, I always tell my clients, "Feel what you feel." Forcing yourself to feel happy when you feel sad doesn't work and just makes the sadness more acute. So, good for you.
And secondly, YEAH!!!!!!!!!!!! You (hopefully) get to go on your trip! You will love all the magic and wonder of Disney at Christmas! It's really a blessing to get to participate in what feels like a pretty major transformation for the holidays. The parks, the resorts, the restaurants... they all get dressed up for the holidays, and it's quite beautiful! And though it might be busy, it won't hold a candle to the week between Christmas and New Year's (I've been during that time, and it's a madhouse but totally doable. We never waited for more than 20 minutes for a ride). Think of the pictures! And the memories! And the opportunities to see Christmas lights at Disney at OFSDL (Osbourne...), on the Castle, and I've got to tell you, the Christmas version of IllumiNations is, IMHO, even better than the regular version. Do you know anything about it? If not, I can tell you unless you don't want it to be spoiled. It really gave me and my family a moment of feeling connected to everyone in the park at that moment, even more so than the regular IllumiNations. I think this could be a fantastic trip, and you'll get to live vicariously through Hope's trip, and she through yours.
Anyway, looking forward to hearing more about your upcoming trip!