Omg, another inept nanny!
Where, oh where are you people finding these girls?

i would be upset with her. road conditions were a bit slippy i understand but if she's near a metro should could have done that instead.
for sure you did nothing wrong OP. Of course she needs to use a PTO day when she's telling you she doesn't want to come in.

I live in DC and my nanny lives near a metro in Arlington. She called this morning to say that it was too dangerous on the roads to come in. I told her that all the schools/offices, metros in DC were open and that if she could not come in she could use a sick day. Is this fair? She was expecting a day off with pay but that is only when it is really impossible to get in-- not when we just get a little snow-- right?

Wow. This should raise a big red flag. Conditions were not bad this morning and she lives near a metro.

I think your solution was fair. My contract states that we will go by the OPM website so it's unbiased. I don't get off for a little sprinkle of snow, but if the roads are truly bad and the Feds get off, so do I. My bosses are federal employees so this has worked out well. My snow days are paid and don't subtract from my vacation.

I live in DC and my nanny lives near a metro in Arlington. She called this morning to say that it was too dangerous on the roads to come in. I told her that all the schools/offices, metros in DC were open and that if she could not come in she could use a sick day. Is this fair? She was expecting a day off with pay but that is only when it is really impossible to get in-- not when we just get a little snow-- right?