Been there, done that. You can't pay bills you don't have. It's also not the honor system here. You're not going to take her word that her half was $150. For all you know it could have been $5. Technically if she doesn't send the items to you certified mail, return receipt, she has no proof that she sent them at all. You can do what you like, but I can't see a judge ordering anything other than payment of the bills, and making a future order for receipts to be sent certified mail within 30 days.
You may also look at the orders, but sometimes it says the word "agreed." This means that if this is some kind of elective medical treatment that BM decided was needed, you may not be required to pay anything because you didn't know about it, and you didn't agree to it.
Attorneys will commonly write nastygrams just like the one you got and will tell you they're going to request attorney fees. Well, you can do the same thing for having to be there. She is the one who disobeyed the order, so any out of pocket expenses are on her.
