I feel your frustration--negotiating relationships with in-laws in challenging at best and we seem to get little preparation for how to do it well. I thought having a baby would make it easier, but it's become more complicated.
But now that I am a mother, I am more dedicated to making the relationships work and letting go of old hurt feelings. Someday I will be a mother-in-law, and I think about how I'd like to be treated. Dh and I come from the same area, but his family does things very differently from mine. I've had my feelings hurt, and it's been challenging learning to recognize the ways his family demonstrates that they care about us and our son. As Mamallama said, you never know where someone is coming from. I know I've done things that were rude without intending to.
MIL never comes to see us, and when I call about bringing ds to see her, she often says, "I don't care." Then we get there, and she's cleared her calendar, bought new toys and fixed ds's favorite foods...
I completely support your need not to be stressed or pressured to participate in showers or other events immediately before or for a while (weeks or even months) after your birth. But I encourage you to work hard to find ways that your MIL can particpate and do things for you while meeting your needs as well. Dh may do a lot of the negotiating, but ultimately, I'm learning the best relationships with MILs are built by daughters-in-law. It's hard, but worth it--she will always be dh's mother and your children's grandmother. Hopefully she will always be your MIL as well.
Can she host a shower that you don't attend close to your due date? If you have enough baby stuff, might she be receptive to doing a children's book shower, a card shower (where everyone sends a card or note), or, if her friends have known dh for years, a memory book shower where they contribute stories, memories or pictures of dh that can become a book for your child. Are there other things that would be fun for her to do that would help or not stress you out too much? Something we do is call MIL a lot to ask for recipes and advice. We don't always do what she suggests. It's a small thing for us to do that makes her feel needed.
If you can, relax, breathe and let some of the stress go. Focus on the blessing of having a MIL who cares enough to host a shower and wants to show you and your child/her grandchild off to her friends.
Having a baby is an emotional, life changing experience, and I support your decision to minimize stress during this time. I know it was several months before I began to feel and think normally again after the birth of my son. Take care of yourself and also remember that if you want the "village" to help you raise your child, it's important to respect the gifts the "village" has to offer.
Blessings to you and your babe,