I know. This one is even more difficult given the grandmother has taken her granddaughter in who is the daughter of her son who she doesn't pay on. (this is Maine -- figuring out relatives is a little more difficult, lol).
I agree we should focus on the two delinquent accounts. Maybe not "take it out" on the 3 yo given it isn'ther fault she is in this family. And, she does have MaineCare, the number one insurance on the planet for the patient.
There was a user on here once (serene?) who mentioned a company whereby in order to set up a payment plan, they have to register their card so it automatically deducts a payment. It's easy to explain to them as you can tell them, "You know it is basically how your NetFlix, Verizon, and other accounts are set up. It works so much better as they have to do something "positive" either the card doesn't work or they delete that account. Then, it is easy to dismiss them right then. We certainly work with people on payment plans, but frequently what happens is they set up $25.00 a month, then they don't pay after three months.
My favorite thing to do is tell them we have no choice at this point but to send you to collections. We are willing to allow you pay half and wipe it all clean. $750 is certainly better than losing all $1500.
The other thing is this mother is very good at using passive-aggressive techniques.