Keep in mind that the nanny does have a life outside of your children. Do not expect her to be the babysitter for last minute evenings out without lots of advanced notice and the ability for her to decline the offer if she has a prior commitment.
Finding a qualified nanny is essential, but it can seem hard to do. What do you ask and what qualifications should they have? What you may not know is that there are services that can help you to find a qualified nanny for your children. When you use these services, they will have already done the background checking and the training. They may be better qualified.