I think you start to advertise an opening in your daycare. The mom isn't telling you about the pregnancy because she knows it would influence your decision regarding the extra day of care. She is hoping she can get you to give it to her but if you know it is only temporary then you likely won't. How do you know that she hasn't already lined up alternate care for the full week just in case you won't accomodate her. This would be the ideal time to sever ties based on sorry you don't have an opening. Advertise to fill even if it is a 3 day week child as two part times pay the same if not more than one full time. My guess is she hasn't told work either and that is why she wants it hush hush as she knows she would never be considered for the job if she was pregnant.