Yes, the nanny will help to take care of the baby throughout the night, unless you tell her not to. For me, I also let my baby sleep with the nanny overnight in a separate room coz I have an older child sleeping with me and my husband. When it’s time for feeding, the nanny will carry her to my room and knock on the door. After I finish breastfeeding my baby, I pass it back to the nanny and she’ll change + coax my daughter to sleep.
As for best arrangement for night feeds, after the nanny, I find that co-sleeping is the best because it allows most rest for mummy :) you can try and experiment and see how things work out for you!