Mother-in-law keeps comparing my five year old to my brother-in-law. Am I overreacting?

My mother-in-law is an extremely eccentric and not-at-all-there person. She likely has some form of Aspergers, is a hypochondriac, and when she visits, we're just as much taking care of her as we are our own children (5 and 4).As eccentric as she is, my brother-in-law (her son, 39) is a huge dipshit. I could tell you all sorts of stories, but let me sum it up by saying that he moved his girlfriend, her son, and their dog into my mother-in-law's 2 bedroom condo, forcing my MIL to sleep permanently on the couch. All the while, he refused to pay rent, made my MIL do the entire family's laundry, dishes, and cooking, while taking what little money he did have to buy a brand new Harley. Oh fine, one more story. Once, when my MIL was visiting us, he threw a party at her condo. It was such a raucus affair that when my MIL got home, she had a letter from the condo board saying that if it happened again, they would have to kick her out. Again, this isn't a teenager. This isn't a single guy in his 20's. He's 39 years old and has a live-in wife and son. I despise him with every fiber of my being.Now, my 5 year old is rambunctious and strong-willed, but she's also smart as a whip, driven, and without a doubt will be a world conqueror one day. I'm biased, of course, but her teachers tell me the same thing. Everyone who knows her, loves her.Like I said, she is strong-willed and has very firm ideas about how things should look. When life doesn't follow her plans, she has a hard time adapting, and we're working on that. However, whenever my MIL visits, and we have a battle of wills, my MIL can't help but start drawing comparisons between her and my BIL. "Oh, William was the exact same way!" or "Lookout, you've got a William on your hands!" Every single time she makes these comparisons, it's like a needle through my heart. I hate the comparisons and I resent her for it. She doesn't see how much of an abusive, ignorant clown her own son is (quite likely) and/or she doesn't see how trying to insinuate that my daughter is somehow a carbon copy of him is insulting.I have thought about saying something to her, but I'm not sure what I should say. She's a very simple woman and it's likely she just doesn't understand why drawing these comparisons would be distressing. But then again, I've had to have some really hard discussions with her before about her son and have advocated for her to stand up to him, so I know she knows he's no saint. I should probably just try to be an adult and not let it get to me, but at the same time, each time she says it I just have this reptilian reaction to it. JUST HOW FUCKING DARE YOU COMPARE MY DAUGHTER TO YOUR ASSHOLE SON. Gahhhhhhh.....halp. via /r/Parenting http://ift.tt/2pmnFy3