I'm with you...but my question is, is she making these comments on purpose?
My MIL does that, too - but she honestly just doesn't think before she speaks. She really, really doesn't. She doesn't mean to be snarky, but she doesn't realize how things sound.
"It's a shame you don't have a basement. Then at least you could confine all the mess to one room."
"Don't worry if your car is cluttered. It's just an extension of your house."
And my most recent favorite, when she picked up the kids to take them to the park, and my DD asked if I was going, too, she replied: "No, it looks like your mommy has a lot to do at home."
Really, it's gotten to the point where it's funny. Though it's mostly funny because I know she doesn't really mean it. Well, she probably means it. She just doesn't intend to BE mean.
I found it really helped me to ask my husband about it, and how is your relationship with your father in law? Or with your husband's aunts, if he has any? It might help to know if she does this to everybody, or just to you. If it's everybody, you might be able to chalk it up as she is just "that" person, and with any luck, start finding the humor in it, too. If it's just you, then by all means, excuse yourself from her company as often as possible. And with other people having admitted to you that she singles you out, you will get major brownie points with the family for avoiding her instead of snarking right back. (And even bigger brownie points when you DO spend time with her!)