NCS here. How do you soothe baby overnight when you are cosleeping? If the answer is “nursing,” then you don’t have a nanny problem, you just didn’t have a realistic sense of how big a transition you were asking for. You are essentially changing 5 major things at once:
1) Caregiver
2) Sleep location (bed vs crib)
3) Sleep position (on side nursing vs. flat on back per SIDS guidelines)
4) Soothing method (suckling vs. rocking/patting etc.)
5) Overnight feeding schedule

You will need to either reduce some of these transitions or expect it to be rough.

If you wanted your child to sleep in a crib at night, you should have put her in the crib from day one and teach her to self-soothe. Changing the game at 8 weeks because you are tired and not getting enough sleep is what is happening. Nanny will or will not get the baby I to a new routine but it will take a while. Your baby is attached and has been taught to sleep with a book in her mouth and a warm responsive body next to her. Husband's usually want their wives back for copulation around that time so that is probably the driving force behind this. I coslept and BF for 2 years but my husband works nights so this worked for us. Figure out what you are willing to give up to.make things work.