I would be applying back saying there can be no change to the payment schedule because you need payment in advance to purchase for the week of care. Also since she failed to provide a proper meal for her children as negotiated you now have no choice but to insist that the children will be fed by the caregiver eating the same meal as the other children in care and that the new fee effective whatever date will be ...... She is the one that brought up reopening the contract so if she complains then tell her that. Also that you not charging for food assumed she was providing a balanced meal for her children and since that did not happen then the privilege of sending the food instead of paying is no longer an option.