Wow, I am totally disagreeing with these answers. The one piece of input a bride has for her shower is who gets invited. She probably should have invited her future MIL, but she's perfectly correct in not inviting people she doesn't know well. In fact, people get criticized for this because of the gift that's required. I always cringe when I get shower invites from people I barely know.
Showers are not family reunions. And if her MIL want to throw one for her "side" and do it locally, she's free to do so, as long as there is no duplication of guest list. She does not have the right to rip into you at all. If she has issues with the invite list, she needs to take it out on the person who made up that list, and with a shower, it is never the hostess.

