Not all MILs are born equal. Some are nasty people no matter what you do or say because you have taken away their baby boy and nobody could ever be good enough for their son. You could join them and make it a really nasty mess or you could find a calmer path and make things less stressful for you and your OH.
Relax. This is the most important thing you can do from start to finish. As soon as you tense up in her presence, she will sense it and she wins from that moment on. Take it all casually - there is nothing more infuriating than a daughter-in-law who just doesn't get ruffled by all the innuendos and outright mean stuff.
Be pleasant. This means backhanding her condescending comments with simple responses like: "Yes, if that is how you feel dear."; "OK MIL, sorry that I hadn't picked up on that being such an important issue for you."; "Really? I can't believe I didn't remember to wash hubby's socks the way you would, how silly of me!"
Ring her up constantly for advice. This is something that puts her on the back foot - she will start to get really sick of hearing your chirpy voice on the end of the line all the time asking for help on the best way to take care of your shared loved one. Lay it on thick and butter her up. Her nasty vibes will be tussling with the know-it-all vibes and that's a match made in heaven.
Buy her outrageously expensive lingerie for gifts. Do it before she does it to you. This double crosses her suggestive notions that you are nothing but her son's fleeting lust craze by pointing out that it hasn't passed your notice that she's as capable herself of all the suggestive notions.
Chill. Do not let this harpy get to you. She is blowing hot air without a leg to stand on. Few men listen to mom when it comes to their choice of lifemate. They may look as if they are listening but really it's practiced politeness that comes from years of experience. Sure, the love is real but the advice taking is not. After all, no man is going to live with mom the rest of his life now, is he? If you feel you need to answer that in the affirmative, time you rethink the whole deal.