What do I need to do to train my nanny?

A few "shadow days" Have your nanny follow you through your daily routine a few days in a row. Make sure you take some time to let her do the routine herself while you are observing so that you feel comfortable she is prepared to care for your baby when she is alone. Show her how to do things the way you feel work well for your little one. Then, returning to work won't be quite so difficult!
Train yourself first. There is a saying in medical school: "see one, do one, teach one". It refers to medical procedures, of course, but equally to taking care of children. Once you are comfortable reading your baby's cues, you can show them to the nanny; once you can do all the things she needs done, you can demonstrate them, too. Above all, watch the nanny to make sure she can do it herself next time.