Her ex husband refused to pay support, yet insisted on visiting rights.
The two should not be conflated. Visiting rights should not depend on the other spouses payment of child support. A child needs to see his/her father/mother, regardless of their ability/willingness to pay support. If the parent is not making the required support payments, then the custodial parent should take whatever *legal* measures they can to recoup those monies. But they should not be withholding visiting privileges.
A parent has a right to see their child. They also have an obligation to provide support for their children. But the two are not (and should not be) dependent on each other.
Leave the kids out of it. NEVER speak derisively of either parent to them.
My parents had a rather messy divorce. And yet, to this day, I am very appreciative of the fact that both of them took great pains to not put the other one down in front of my sister or I.
The Wolf