L.G.
I didn't experience the same situation but had a mother in law who kept popping over uninvited right after baby was born.
I was hormonal, tired and not in the mood. I needed time alone with my new baby.
I took my baby, went to my bedroom to nurse and nap. Even if we weren't napping, no one needed to know that, I would just bond with her in the privacy of my own bedroom.
Just tell your Mom that you and baby are going to your room to nurse, nap or enjoy some bonding "mommy and baby" time. Tell her you'll come back out at a certain time that you decide upon. It's a subtle way of leaving the room and letting her know you want some privacy.