JB,
I know a lot of docs; few if any of them will get involved in such a situation between married parents fighting over a child's medical directives. What you have suggested is determined by lawyers who fight back and forth as to who gets to be the primary parent and/or in charge of medical decisions, typically during divorces. Based on what I've read, Mr. WILL fight it. An end run is bad form, and it is likely that the medical profession will ignore such an end run until the lawyers fight it out.
That's why I stated that, if this is her decision, an attorney specializing in these matters should be her first stop.
Making ultimatums almost always backfires (google it). That's why you have suggested. Is it really worth fighting over a few meetings to make a quid pro quo/ultimatum? If their daughter hates the meetings as much as she says, this will take care of itself. Given her age, that too will take care of this situation in a short period of time. Making it a reason to fight, in this instance and IMHO, is ill advised. Using up that much political capital in this matter is not wise, IMHO.
There are bigger issues to fight over.