You are correct. The Bride knew her friend’s son had behaviior issues prior to asking her to be the Brides’s Maid. It is the Bride’s mistake in not covering this issue at the time she asked he friend to be part of the wedding party. Bringing up up just prior to the wedding shows she was thoughtless about her friends most important family member/child.
All that being said, we have a supposedly autistic boy in our church. His mother is a child psychologist. I thing the boy needed to be told how to behave at 2 though 5 and now at 8 it is too late. Therefore she calls it autism and is creating a mentally ill child. The kid will be messed up in other ways as the dad is the most whipped milquetoast guy one can imagine.
It doesn't sound like this was brought up "just prior to the wedding." The wedding is this summer and they decided early on not to allow children, and she feels her friend has had "ample time" to make arrangements for childcare. The friend is asking repeatedly for permission to bring the child who is known to be disruptive at major events.