Our new nanny has an odd issue, how on earth do we approach this??!!!?

You have to decide whether you can deal with the odor or would rather ditch the nanny. Telling her she smells will just embarr her and maybe cause her to leave. If it's her feet that smell, leave a bottle of tea tree oil foot spray somewhere visible. It's all-natural and hippies love the stuff, which is good because it really helps stinky feet.