I did end up messaging her and telling her that my rules state that I am paid the daily rate for the time they were "supposed" to be here on Monday, and that just because the grandmother has offered to take them, pay is still to be received. I explained that I am not in the position to lose money because someone has offered to take her children. It's always been in my rates and rules and that's what angers me sometimes, they know and yet they still try to get away with it.
I think I may redo my daycare package that I send home with my daycare parents to more clearly state some things so that they cannot question me.