She should feel some of the hardship of the choices she is making. Not to be punitive, but fully realized accept the consequences of her actions. Financially, emotionally. socially, etc.. You are not her lap dog to baby sit every time she wants to go out and socialize. Get even reciprocity with this and set some boundaries and solid communications that you will not change your plans or days with the kids, unless you are given notice well in advance. At least 2 to 3 weeks in advanced, and make sure you get an equal swap for those days in writing. Otherwise they will keep asking you last minute to drop your plans to watch the kids, while they get to go out with friends and potentialy pursue other people.
