Well, it is fine to say no kids, and her reaction rude, but she also has the right to feel that she should not be at home alone so her fiance can attend and she cannot.
Can you help her to find child care? Can you suggest someone she can hire to stay at the hotel with the kids?
I think if you stay rationale she will be the only one to look foolish. Try and be supportive, but do not change your mind as to adults only.
When we renewed our vows I wanted kids because I wanted the kids to see marriages can work in the day when divorce rates are so high.
Just remember it is your day!