Re: Paying for private school
This is an interesting problem.
First off, unless you have been specifically required to pay for private middle or high school, you have no obligation to pay. If filling out a financial aid form puts you in agreement to pay in any way, you should refuse.
If you resist this, your daughter will of course see you as the bad guy.
The court probably needs to be invoked in this, though technically, you have to file it correctly. You don't want to seek a modification declaring that you are not liable.
The other posture available is "contempt." The "contempt," or refusal to obey the court orders and judgments, would be your ex's failure to obtain your consent and agreement to this expensive plan before discussing it with your daughter. For this to work, you really need to have shared legal custody -- the obligation to consult with one another over this plan.
I know several good attorneys who practice in Hampshire college, and would be glad to give you names. It is important that this be handled delicately, and that the pleadings be well done. The Hampshire court is does not always operate as Eastern Mass. practitioners expect, as I learned from one foray into its chambers, and you need someone familiar with it.