There are several ways to handle it:
1. If you have to work, nanny has to be there, take a paid day or take an unpaid day if there are no paid days accrued.
2. If the commute is 30+ minutes and your school system is closed, nanny has the option to not come in if roads are too bad.
3. If you absolutely must have your nanny work regardless of weather, you need someone with a <5 minute commute or a live-in.