Our nanny has bad breath :( Could this harm my baby in any way?

It is not directly harmful to your baby, but it may be a sign of a major illness. I would be uncomfortable if my baby's nanny had bad breath.. https://en.wikipedia.org/wiki/Halitosis

There is no harm to your baby. However, if you feel uncomfortable to let her handle baby with it, you can try to request if she is okay to wear mask.

thanks