I'd like to slap my MIL

For the past couple of days my MIL has just been grating on my nerves something fierce.
Today was the icing on the cake though. I got both our kids off to school, and a couple of hours later my daughter calls to tell me a bedbug crawled out of one of her books in the middle of class, which of course caused quite a commotion in class.
It has been a few weeks since we treated the house and roasted the bastards out and up until today we had not seen even one. Well Thursday afternoon she insisted that she bring in this wicker box thing that had been taken out of the house while we were clearing the house out for treatment. My husband and I BOTH told her if she brought it back into the house she would be bringing the bed bugs back in the house, because despite how well you treat it, if you don't put it in a room and seal the room off and heat it up to 140 degrees for at least an hour, you won't be able to kill bed bugs off on wicker stuff. We know because we treated our wicker headboard to our bed 3 TIMES spraying it down with chemicals till the headboard was completely dripping with chemicals, and they STILL kept coming. So we threw it away, we had no other choice. It was either that or continue to be fed upon daily by these horrible mini monsters. But NO she, miss know it all that she is, INSISTED that it was just fine and brought it back into the house. Well of course, our dog stays in the room that she brought the wicker thing back into. And we had a thunderstorm, which our dog absolutely is terrified of, so he went into my daughter's room and hid under her computer desk, after having been laying beside this wicker thing for several hours. We KNOW that what happened is a bed bug came out of this thing and hitched a ride into our daughters room, and because her bed is set up to prevent any bugs from getting onto her bed, it had no choice but to hunker down in one of her books on her bedside table and wait for an opportunity to feed.
So when my daughter called me from school to tell me about what happened, I told my FIL right away. It wasn't long before my MIL called to see what everyone was doing, and he told her what happened. And when she came home she called my daughter into her room to talk about it. She completely denied that it came from this house, that it HAD to come from some where else. That would be feasible, if my daughter had spent the night somewhere else anytime since we had treated the house, or had even gone visiting someone else's home at anytime since we had treated the house, but she HAS NOT. Even my daughter asked her "Well if it didn't come from here, WHERE could it have come from?" She got told "I don't know but I know it didn't come from here." My daughter doesn't even use the lockers they provide at school, so it isn't like one was hiding out in her locker waiting to hitch a ride or something.
Needless to say that was not ALL she had to say to my daughter. She got the old "Well I don't want to talk bad about your parents, but" routine. She is 14 now, and has seen enough out of my MIL to know that she is full of shit. My MIL sat there and told her what bad parents we are, how we sit around and do nothing all day but sleep, and god only knows what else she actually said to her that my daughter didn't tell me.  She already knows that my MIL is a compulsive liar, I mean what else do you call someone who lies about shit she has not even been asked about. For example, the other day I walked into the kitchen. I had not even said a word to my MIL and she goes, "I don't know what we're gonna do, I have $10 to my name to get dinner for everyone." I told her not to worry too much, that we would make do as best as we could, just like we always do. Later on that afternoon she sent my FIL out to the store, well when he got back he forgot to make sure he grabbed the receipt out of the grocery bag, I saw it and looked at it, and lo and behold, he had paid $50 in CASH for the groceries. That's what I'm talking about, I could understand sort of lying to me if I had ACTUALLY asked her a question!!
But like I said, my daughter sees the BS, hates it as much as we do, but what can you do when you're stuck like we are, with no other place to live?
But what got me was her complete denial of the fact that the bed bug came from her wicker thing, or that it could have even come from here. Not to mention she could have cared less how mortified and completely and totally embarrassed my daughter was about the whole school-bed bug fiasco. Not even a "I'm sorry you were so embarrassed." She could have at least done that, even if she wanted to continue denying that the bug came from here. At least TRY to make the girl feel a little better. But no, she just switches gears and starts talking shit about her parents...what the hell kinda grandma is this crazy bitch anyways!?!?!
I swear I always try to think good about people, and to never think really bad stuff. But tonite, and I feel SOOO bad about this, I swear I do, I actually wished she would die in her sleep. Just go to sleep, and don't wake up, and spare us all this torment you constantly put us through. Spare your husband the constant controlling, hateful way you treat him, spare your son the spiteful, hateful, petty way you treat him, and spare your grandchildren the hate filled speeches about their parents. To hell with sparing ME anything, it's not about me, I have put up with abuse from more seasoned abusers than her, so I can handle it. But the way she treats others in the house is just atrocious. It's like so long as you are not related to her, she's ok being truly nice and kind. But God help you if you are related to her, because you are a viable and, in her opinion, a valid target for her to attack. It's like, just because you are related to her, she feels she has the right to talk to you any way she pleases, and God help you if you have to live with her, because then, she feels, she has even MORE of a right to treat you however she feels she wants to. As bad as I feel for my kids and for my husband, I feel even worse for my FIL.  She thinks nothing of announcing to the household that her and my FIL have not had sex of any kind for two years, like that's any of my business, and right in front of my FIL to boot! Not to mention the way she talks to him, calling him all kinds of bad names, and poor fella, it's not like he has anyplace to go to get away from her hateful treatment even for a second (cause she won't hesitate to follow him out into the yard continuing to talk to him hatefully), and certainly doesn't have any other place to live. So in a way I feel worse for him than I do us. Our son has already had her figured out a long time ago, and although it IS rude, he don't hesitate to tell her she's being a jerk or an ass when she is..lol
I just feel bad for having wished the end for her, and just so frustrated as to why she has too feel this need to lie to me, when none of us care what she has money wise, and none of us care if she buys take out, instead of eating what she buys for us to eat, even when she cries broke all the time. We just DON'T CARE and she just don't seem to get it. I'm truly about at my wits end with this woman, and my husband is terrified, wondering when me and her are going to "go at it" again and fight. I can understand his fear, after all me and her have already had two knock down drag out fights, but he just don't seem to understand that I have gone past the point of caring, really. It's really not worth it to fight with her, not to toot my own horn, but each time I have fought her, there really hasn't been any "fight", she's old, and past her prime, and can't beat me in a fight, unless she brings a weapon into it, and even then I don't think she's got a winner. Hell the only reason we got into an actual fight before was because she put her hands on me first, trying to beat me in the head and all.
I'm just so frustrated, and I'm starting to think she truly has mental problems, like she might be bi polar or her mood swings might be from taking narcotic pain meds, hell I don't know what her problem is, I just know she's got one, and that she IS one.