I would just leave things and ride out the days. You could bring it up at drop off or pickup with a reminder like this will be your last payment or as of whatever date I will have all of child's things ready for you to take to your new caregiver. That way you will know by her reaction if for any reason she never got the letter. If you gave it to dad then come right out and ask him to make sure he made the mom aware of the situation too. That should also get you some information on how they are doing in the finding new care.