ETA: I just read some of the other responses below, and it seems to me that MIL's behavior is not simply a product of her husband's current medical issues. It sounds like she's been this way for a long time and has done this to you before. It sounds like a power and control issue. Yes, she may be concerned about her husband, and that may exacerbate her behaviors at this time, but if you truly don't like someone coming into your space and trying to take over, you have every right to limit that. If she really wants something to do and you truly don't mind her doing some things, work together to identify a few easy projects to keep her busy (mending, comes to mind). You could also take her to your library to get some new books and magazines to read to help occupy some of that time. Ask her to play games, draw, or read books to her grandchild, or maybe take a walk with him or take him to the park.
ORIGINAL:
She does it because she can. I realize there are two sides to every story, but if she's even have as annoying as portrayed here, that would be enough for me.
So, you limit her ability to meddle. Kind of like toddler-proofing a house, except for mother-in-law-proofing the house. First, tell her firmly, (not defensively or angrily, just firmly) that she is not to go in your bedroom and get/do your laundry. If she does, start locking your door. Make sure she has no access to a key for the door. If you can't lock your door, lock the laundry in the trunk of your car. Really. This will send a strong message to her that she isn't hearing through your words, and it will also stop this one particular behavior that bothers you so much. Gather your son's laundry and put in in there, too, so the only laundry she'll be doing is her own.
If you really don't want her cleaning things, limit her access to the cleaning supplies. Put them out of her sight in the garage, or you could also lock them up as well.
If she wants to make meals, ensure that only very simply ingredients are around. When you're away from the house, don't answer the phone every time she calls you. Let her leave a voice mail, and if it's important (like the house is on fire, or something like that, then you respond). You don't respond to phone calls about how to make spaghetti sauce. You just do NOT engage in non-essential interactions with people like this.
If she says how tired she is, tell her to go lie down and rest. If she doesn't, that's on her.
When she orders you around? Remember, you're an adult. You don't have to follow her orders. I think you may be forgetting that and handing your power over to her. It's kind of like you're allowing yourself to be her victim in this case. Not saying she's not annoying, but you don't have to play this game, you know?
As for the criticizing? Nobody likes to be criticized, but it sounds like she does this because she knows she can get away with it with you. When she criticizes your methods, you can calmly, firmly say things like "This is how I make baked chicken. You can make your recipe next time." Then, let it go. Yes, that is very, very hard, but why engage with someone like this? If you know your house is clean, your family is well-fed and thriving, then her criticisms aren't accurate, are they? It's just her running her mouth. If that's the case, her continued criticism of you only reflects badly on her, not you. Reminding yourself of that can help you keep it together when she's doing this.
What does your husband think? Does he see this, or does she only do it when you and mil are alone? At some point, if she continues her constant criticizing, he should step in and have a talk with his mom.
Finally, the sooner you and your husband can get into a house of your own, you'll feel less like you're under her thumb.
Stay strong. You don't have to play along when she's acting like this.