Hi OP, You have a good package going on there and super considerate to also offer COVID days for your nanny. You got some pretty good answers here. i would also add that, you should consider including the inclement weather clause and what guidance you'll use in your contract (eg OPM, DCPS or MCPS guidelines on weather). It makes things so much easier as everyone knows what to expect when inclement weather comes up. You are prepared as well as you nanny and she won't feel like she has to take a risk to her safety to be at work so that she gets paid. Other people refer to them as snow days or random off days as above. Either way they don't come out of her PTO or vacation time because she did not necessarily plan or request to stay home & not work.
From my experience, this is something that falls under guaranteed hours to cover inclement weather or weird unforeseen circumstance like city shut down or something. I've worked for families where it was mutually discussed as part of the contract and honestly it made me feel valued as not just a person but a nanny especially in situations where parents are not essential workers & the commute is NOT within safe walkable distance, roads are too dangerous to drive or take public transportation on.
If she is live in or lives within a 5 minute walk or so, perhaps that is a different scenarios where you can both agree for a work day. As for parents who are essential workers, I know some families who mutually worked out for their nanny to spend the night over so that she is safe and they are guaranteed child care. But you have to take into consideration if this is a nanny who is single/married, has children etc and also bear in mind that her spending the night is benefiting the job as well. Perhaps those who have experience with this can chime in.
All the best