My lovely MIL sat front and center, in front of the gift table, and scoffed, laughed, rolled her eyes, and otherwise made fun of every.single.gift that didn't come from her family. Thankfully, her back was to 95% of my guests, so they couldn't see her. It would have been humiliating had they been able to see her.
She, along with her mother and sister, barely spoke to me (except to make a ridiculous show of hugging me "bye" in front of my family when she was leaving), and completely ignored my hostesses, my sister, and my mother.
She acted so horrible that I had at least 3 people ask me if I'd like them to remove her. I had a horrible case of the 24-hour flu the day before my shower, and had no energy to deal with it, or I would have taken them up on the offer. I just ignored her, but a few of my friends made a point to tell hubs how she behaved. (he showed up at the end of the shower and could tell something was up. These friends called/text hubs later that evening because they were so concerned) He's since given her an ear-full about it, but it still made for a miserable day.
Had I been feeling well, that woman would have been escorted out. I just wasn't up for the drama.
Other than the MIL show though, my shower was beautiful, my family and friends were wonderful, and I had a great day despite feeling awful. I just tried to focus on the happy parts of my shower and ignore the MIL downer.