Jen, it is actually normal and healthy to super strongly dislike what your kids are doing at times. Even though you love the kid with every fiber of your being at the same exact time - you STILL want to strangle them!! Our kids can push our buttons faster than any other person, being or thing in the entire universe except our mothers. And we CAN learn to ignore our mothers. Not easy, but possible or so I am told.
As for will she stop wetting the bed? MAybe yes, maybe no. Did she ever get tested for the tethered cord? If that isn't addressed the bedwetting won't stop if I understood the docs in Oregon. It will also cause/contribute to many other problems. I know that she freaked on the MRI. Make the appointment to have her either sedated or anesthetized for the procedure. To sedate her they will give her something like versed (very strong benzo - awesome stuff that mostly only the anesthesia people get ahold of). If benzos are a problem for her, or she will fight the sedations (it is to make them calm and sleepy but not put them under), then insist they anesthetize her. Yeah, she will fight the iv and the medications, but they will get her out and do the test. Jess had to have this for the last MRI. She was out for the test plus about 5-10 minutes. She was groggy and not coherent, but it wasn't a really big deal. NO reason why it cannot be done for your difficult child that way.
You will likely have to get the docs to justify it to the insurance co, but they can. If the copays/coinsurance is a problem, go to the dept of health and human services website and see if they have waivers to help sick kids with medical bills. It would give her medicaid and the insurance her dad has, which would mean no copays. I don't know if she is eligible, but don't just assume she isn't.