I have cared for a brittle diabetic, such as you are describing. We had to check her blood sugar every four hours, around the clock. If she hit 200, it was time to eat--no exceptions, as she would go from 200 to unconcious in less then 30 minutes if she didn't. If she was in the 300's during the night, we'd recheck her an hour later--usually because she was beginning to trend downwards, but not always. A blood sugar in the 400's was a "safe" range for her.
No, it's not normal, no it's generally not healthy, and every other diabetic (including my spouse) would feel like total crap in the 400's. Most are lethargic and have a headache, digestive upsets, etc at this poing. Not this little tiny lady.
It also took very, very small amounts of novalog to maintain her. 70/30 and Lantus had been tried with her, without success as even small amounts made her very difficult to maintain.
Just wanted to point this out, that despite all of the information about diabetes that we have, and the "rules" of how it's supposed to work, there are exceptions. And on the diabetic support message boards, there is a saying "your own mileage may vary". Which I have found to be very, very true.
I wouldn't bat an eye if my DH gave himself 35 units of novalog before a big meal (he doesn't anymore--thank God for the insulin pump!) but I recently had a pt. whose sliding scale dictated I give him 25 units, and yeah, I was hesitant to give him that much, but his blood sugar at lunch was 304.
Again, trust the nurses that know this pt, they have worked with her for a while, and it sounds like she is the exception to all the diabetes rules.