I am going to approach this as a nanny for over 10 years. I called into work one day when the snow was coming down so hard that I could barely see the end of my short driveway. I called my employers to let them know that I didn't feel comfortable driving to their house. The dad was pretty annoyed (he worked from home), and gave me a hard time. Mom called me 1 hour later to apologize, and say SHE was going home half day anyways due to the storm. I do not call into work unless i Have to.
Does your nanny have a certain amount of sick days allotted to her? I have 5 sick days/5 personal days. I am ONLY allowed to take my personal days on days that are PREPLANNED. Mind you, I am also paid 52 weeks/year, whether the family uses me or not. They view me as a professional, if I worked in an office, on salary, I would be making the same amount every week.
I would sit down with your nanny, and say "I realize the weather was bad on X day, but I really count on you to be here on the other days. I fyou need to take a day off for personal reasons, those need to be PREPLANNED!!!"
Something families that employ nannies don't understand is: You risk losing your nanny if you don't give her room for personal or sick days/year. Or try to cut her pay for having to take a sick day. Business world people get those, why not a nanny.