I know this is late, but my sister is a nanny. With one family she would go with them on vacation but she was to work the entire time. If you do that, spell out the duties. This was one reason she left that family, as the family had her working 24/7 during the vacation and did not pay extra. They put the kids in her room, and they refused to do anything with the kids. one time the boys was vomitting the entire trip and she had to deal with it, not the parents. So make sure if you take the nanny, she is doing the same duties she would at home, and if more, you pay her. they felt since they paid her way to get there, she shouldn't have any relaxing time.
This family now, they take several vacations in the year. She is paid every time, but they still have her do some work. She takes care of their dog and will do things in their house. Nothing that is more than about 2 hours a day, but still something. She may do laundry, or clean the house, rearrange the kids rooms. Clean out the clothes that don't fit, and toys that they don't use. Since she is still getting paid, she doesn't mind going there. And then she can more or less chose when she goes into work.
If you haven't set up anything with her in regards to vacation or sick pay, i would consider that at her 6 month review. A lot of jobs don't give you those things right away, so at 6 months when you give her the raise, you can let her know what she is entitled to.