Planning around other people

I have young kids and own a business as a Life Coach. I have a nanny that watches my kids a few days a week while I coach and work on my business. Those few hours I hit the ground running and plan and work incredibly smart to maximize the time. I plan it all in Monday Hour One very carefully. Today my nanny told me she was sick right before I needed her. Without her, I don’t have those precious hours to work on my business. How do I plan for when things like this happen?