Julia, the problem here is that there are extensive PAST medical bills that the ex has refused to pay, ChatterBox has tried in the past to get her to pay and the AG's office said she filed proof of payment so they refused to act. It's a lot of money and he can't exactly give up on it.
Not to mention that once he stops paying half and expects her to pay without getting the payments sent straight back to her, she's going to stop paying her half and the docs are going to come against him anyways, this time AFTER the fact, when he's moved on and got other, new expenses to deal with... and he's STILL going to have to get the court to intervene to force the ex to pay for the unreimbursed medical expenses.
This poor little girl has a serious health problem that causes her to be incontinent at embarassing times if her diet is not strictly kept, and the mother has made it worse by not following the diet, sometimes actively sabotaging her, and for a while, kidnapping her and not letting her see her dad at all. After the whole custody issue was straightened out, she was not allowed to have control over the kid's health care any longer, which gives you a clue of HOW bad it got. Yet she still went to the school to bring lunch to the kid every day, lunch that did NOT follow the diet and only made the health problems worse...
The bills have got to be staggering, and the fact that he has shouldered teh whole bill so far with her PRETENDING to do so and getting it all refunded to herself is ridiculous! He can and should pursue payment... I don't think trusting her to pay her half is a good option once he cuts off her ability to get it refunded back to herself. It'll just delay the whole process of enforcing the reimbursement order and put him further behind on finances.