I think I might have PMed you a few months ago? A lot of this sounds familiar.
Anyways...I can't advise you on the nasal spray or surgery or diet. So that's like the majority of your questions. I'm sorry.
Tegretol is usually used for complex-partial and temporal lobe seizures which sound like what you are describing. IME, If she is at a therapeutic dose or at the upper level of dosing, and still seizing, that is when docs start looking at other meds. Or adding meds.
I've had experience with too much medication causing myoclonus (jerking of limbs) but not loss of muscle tone. And I don't think it was from too much tegretol but I can't remember.
I don't know what you mean by a "seizure focus in her brain (the malformation)" ?
To the best of my understanding, Seizures start in one part of the brain and stay there until they stop...or generalize, meaning spread throughout the brain (secondary generalization). Focal seizures stay in one part of the brain. If you are saying her seizures are due to a malformation, definitely ask what her options are, if surgery would help. There are also devices that can be implanted to help deal with seizures. They're vagus nerve stimulators, if you want to ask the doc. VNS.