Just keep smiling and being disgustingly polite. It will drive her wild but there will be nothing she can do about it.
Take the passive, ignore the aggressive. She'll either stop or blow up. The latter would give you a chance to have it out properly.
You don't... Move to Florida or the local equivalent and don't lend them money. :)
OK... Having been through the multigen house thing I get what you are saying. And as the grandparent now I get how you feel and you are in a bind.
Things to consider: She may be suffering from post partum depression. So is this behaviour very different to how she was before the birth?
Or, you may be in the middle of a territorial dispute. Old Chinese proverb say that two women under one roof equals trouble.
Or maybe she is simply a lazy @$$ed b*tch who wants you to do it all for her while she watches daytime TV.
So start by thinking that through and be honest with yourself about it.
Then decide what course to take. Remember if you want change you are going to have to be the one to adapt. As far as she is concerned things are fine. And a warning.... DONT get on your sons case about this or he may very well take her side for peace and quiet and leave you in a worse position. Just quietly decide and deal with it.
Stay assertive. Show her by example.
kick her *** once. and make her realize whose the boss. then make sure you car about her?