Speak to your husband. Let him do the talking. Both of you must be on the same page. This reduces the tension between you and you mil. Alternatively, you can also ask the confinement nanny how to discern the cries of the baby, and indirectly both u and your mil learn together how to handle. Then once in a while when mil is in a better mood, can seek her help with the diapers or help with feeding.
Be firm and tell her to let you handle so you can learn as much as you can from CN. Tell her NO and or just stay in the room and lock the door. Sure she can complain to your husband, but in the long run, your sanity is more important. Make this a habit, next time when she decided not to ‘take care’ of your nb, your life will be very miserable.