Regretfully, verbal agreements cannot be enforced. And, even if CS was waived, it can be opened at any time. There are many cases were spouses gave up tens, even hundreds of thousands of dollars in assets to waive CS, to have to pay it anyway. Federal and state laws overide those agreements.
Is there a parenting plan in place? If she is being denied time, she can go to court to have it enforced...but expect the child support order to follow.