Where did I put my straight jacket?

It's been a rough week in my household.
For starters, I am pretty sure that I have a cyst on one ovary, which is making everyday life quite a bit more painful than anyone would like.
You know how animals can sense when you aren't feeling well, and they seem to go out of their way to try to comfort you?  I think my kids sense it, too.  Only they are doing their best, it seems, to put me in a mental ward before the week is out.  In fact, the thought seems pretty nice right about now.  Soft padded rooms, nice sleepytime meds..ahem.  Sorry.  Back to what I was saying.
Besides filling my days with the normal wife/mommy stuff, the kids have been into all sorts of mischief.  Mostly Madi, though.  I am not sure why all of a sudden she has decided to act in this manner.  I know, I know, ALL kids have bratty streaks.  I get it. Doesn't mean I have to like it.
Here's just an example.  Yesterday Madi decided to take the poop out of her diaper and smear it all over the place in her room.  All in the amount of time it took me to go to the bathroom myself.  She made sure to get it ground into the carpeting really nicely, too.  After cleaning that mess up (and let me tell you, Resolve carpet cleaner mixed with feces makes for a vomit-inducing scent) Madi decided that she was going to beat on her sister and the cat for the rest of the afternoon.  She was in time out at least 5 more times.  And this was all between 4 and 6 in the evening.  She pulls hair, she slaps, she kicks, she pushes, and she takes stuff away.  No disciplinary method has worked thus far.  I know that the part of her brain that controls decision making and impulse control was damaged with her strokes, but I know she knows right from wrong.  Not to mention that none of her team thinks that the amount of damage done is permanent.  I am at my wits end with her.  I love her SO much, and it makes me so angry, sad and frustrated that she acts this way.  What am I doing wrong?  If this goes on much longer, I may need one of those "special"  jackets.. you know, the ones where you hug yourself?
I feel like a parent failure a lot these days.
I am so afraid for what school will bring.. I don't want to be the parent of "THAT kid"; you know, the one no one wants to play with or be around?  But yet I fear that's what will happen.
Tomorrow we will be heading for the Mayo Clinic for yet another checkup.  I will be happy for the reprieve, as Sydney will be at a relative's house and the cat will be at home of course.  Madi will be happily strapped into her carseat, where she cannot be mean to anyone or destroy anything. 
Ninety-five miles there, ninety-five miles home.  Seems like a perfect time to restore my inner peace.
And thank the Good Lord above for in-car DVD players.