In my case, where my ex moved out of state during our separation the court mandated that he can have all the visitation he wants (within reason) in our state with prior notifiaction. As far as visitation outside the state it is to be decided by the children as to what they want to do. I now at some point have to pay for them to travel to see him but am fighting right now as my daughter at 6 (no experience flying) is too young to travel alone. My ex said he cannot afford to fly here and back with her. My son is only 3 and cannot fly alone without a parent until he is five.
I made it a choice for our kids as I don't think a child should be forced out of their comfort zone to travel. If they want to go then I have to let them.
I don't know why you all would have to follow her, I would say what is fair is you alternate paying for her to fly in to see the kids to make it easier on everyone. A plane ticket gets her there faster, less money and not time wasted in driving. I am very accomodating to my ex, only for the children's sake, as far as picking him up at the airport, allowing him visitation here at the house with them or to take them wherever while he is here, providing him use of the mini van so he has carseats. I would go back to court, with your husbands medical conditions documented. Try and go to mediation so it costs less but devise a parenting plan. You do not have full custody if she has visitation, you have primary, there is a huge difference.
I would say if she moves over 200 miles that she is to arrange coming to see the kids, or a reasonable distance.
It isn't fair you all have to accomodate her moving. I certainly won't for my ex. I encourage visits and when the kids are older allow them to go there alternating holidays and in the summer. I made it a huge deal since kids are settled here, he left and the kids are in school that he has to make the effort to come here during the school year if he wants to see them. At some point I will have to put them on a plane to see him and split the cost of traveling with him. I am sure he will see to that, it isn't fair since he is the one that left, but that is how it is sometimes. The main goal overall should be making sure the kids get fair visitation with both parents and their needs are put first.
Hugs, it sucks! I know firsthand.