I am so sorry to hear this. That is terrible. Sad for the little girl and her family to be going through this, but also sad for you that you will miss them so much in sharing your big day with you. I too am going through kind of a similar situation, not any children sick, but fiance's two sisters and their families probably will not be able to make it, due to unforeseen circumstances, to our wedding either so I an understand how it puts a damper on the wedding plans. I am feeling like I should not be happy and planning my day without them... but what do you do?
Hoping for the best for the little one's full recovery.
Hope you are able to enjoy your special day.