Yes, keep it brief and to-the-point. "Less is more." It should be a COURTEOUS read, tho -- matter-of-fact. You don't want to come off like an ass. If you want, you can run it by us first.
Take the opportunity that this WILL be in writing, to state that you "will continue to meet the family's needs and obligations," as a CYA. Which kind of goes to "what you owe her" question.
Legally, a family court judge may end up ruling for her to be able to continue "in the lifestyle to which she is accustomed," and that can easily include both wants AND needs. But until that is ordered of you, I would strongly encourage you to meet ONLY the "needs" portion of that, and certainly NOTHING that constitutes ANY enabling of her decisions to run away from the marriage and the family.
When in doubt, err on the side of generosity, with that last noted part as the exception, of course.
