Don't be embarrassed. My approach (blame my family), stare directly at your mil as you get set up. It's pretty mean to exclude or shame a mother for normal maintenance/need. You should absolutely give her a reason to be uncomfortable.
But you are pumping not breastfeeding and you are in her house? I think you reaching here… her request is not crazy.
Sorry you had this experience. It’s sad she made you feel embarrassed about doing something natural for your baby. It can be very isolating when you have to constantly leave the room to pump or nurse and sometimes it takes awhile. If it makes them that uncomfortable then consider not visiting during times when you need to pump or feed. If that’s even really possible.
I wouldn't go there anymore. Their lost.
I can understand both sides of the story.
That’s terrible! So sorry that it’s happening to you. Did your husband have any input?