No, unless she's been ordered by a court to provide an accounting she doesn't have to do anything. However, the beginning of co-parenting is cooperation. Having spent years teaching court ordered classes for high conflict divorces I'll be the first to say just because you can legally do something doesn't mean you should. The system encourages combative parenting, doesn't mean we need to play into that system. If the ex's request is out of a desire to know how the money is being spent because he cares about his kid it's not unreasonable. There certainly may be times when there are other motives and that's a different story. But again, you have to consider the big picture. There's almost certainly a time when the child is going to want something that might mean having to ask dad for a little more than the court ordered. Now he's perfectly within his rights to refuse to pay anything above the court order, and when you've been behaving that way you can't be shocked when he does the same. As any numbers of studies show, when dad is actively involved in the child's life (not simply the visitor the courts would reduce him to) he's more than likely to go above and beyond the court order. But absolutely, if she wants to be a combative parent then she can and so can he. Then we all get to pay out of pocket every time their disputes end up in court hearing after court hearing.