OP here: Thank you everyone for your input. It's greatly appreciated! Will take it all into consideration and see what to do next
To anonymous poster at 14:35: She does get breaks. She's not fully taken over care for both kids at the moment since I am home on maternity leave and my 22 month old naps for 2 hours in the afternoon. We have also told her that her break is important so priority for her is to make sure she eats and take a breather when both kids are sleeping. We have noticed that our newborn is a (good) napper and takes 1.5 hour naps 3-4 times during the time the nanny is here and even with the 22 month old awake and around we felt that she may be able to continue some of the basic child related tasks that she wants to drop. Plus, I have spent few weekends alone with the children, it is definitely not easy, however, she is a nanny who signed up for this and agreed to take on this task/challenge when we hired her. I still appreciate your tip though.