OP, I am so glad you made the decision you did. What a good parent, to sacrifice all the planning you made over 18 months to ensure your daughter was able to really enjoy it, and you wouldn't be worried about her health!
I had pneumonia as a child at Christmastime and was dearly upset that I was to miss a planned day with my older, married brother and his new wife: going to cut down a real Christmas tree (we always had a fake one, and my Mom would spray pine scent around and tell us it was the same thing) - and then off to the newlyweds' apartment to bake Christmas cookies. All of my sisters went, and I had to stay home.
I well remember laying on the couch, looking at our Christmastree and I literally was too weak to get up. Not only could I not have hiked through the woods, I really wouldn't have been able to stay upright enough to frost cookies. Weak as a kitten!
Please let us know when you finalize your arrival date in October - we're leaving on the 23rd and I would leave a gift for your daughter if we crossed dates.