Good question from Avvo recently:
I live in New Hampshire; the divorce and child support were determined in Massachusetts. New Hampshire does not require support of an 18-year-old student; Massachusetts does. We changed some orders in New Hampshire when my daughter went to live with her dad for a year in Ohio. She has been living back in New Hampshire for the last three years. My daughter is a college student and needs the financial support that her father can afford to provide. [Which state’s] child-support laws govern her support?
If the original decree occurred in Massachusetts, then that is the law that should be applied. The mother in this situation could attempt to suggest a change in circumstances – but she would be wisest first to retain an attorney to review the facts and circumstances of her specific case to see how that applies.