I'm quite upset about this, as I did everything by the book. She was a California king hatchling. I used proper substrate, kept a temperature gradient from 73-86F with two thermometers to make sure. I fed her small, properly thawed pinkies and kept water available to her at all times. The humidity in the cage seemed to be about right.
The morning of her death, she was somewhat sluggish, but still responsive. I'd seen her like this before, especially when I first got her, so I didn't think anything of it. That night I reached into her cage to feed her and found her completely limp and no longer breathing.
She has no sign of mites or similar. In the month and a half that I had her, she did not shed, nor did she show any signs that she might (no blue eyes, etc). Also she defecated very little (as far as I know... she was my first snake, so I have no idea how much they're supposed to... er... pass) though I would give her warm 'baths' to get her bowels moving after I heard that constipation can sometimes be fatal. The vet said it was nothing to worry about, though, that small snakes don't really excrete that much.

I don't have enough money to have a postmortem done, so does anyone want to venture a guess for me?