Sorry to hear about that. I don't think it was your fault at all. You did what you thought was right, and from reading your post you seemed very smart about taking care of it. I'm not sure if she was in deep brumation or not... that is very weird. I would think she would "wake up" if you warmed her up a bit or something.
I know a time at the vet's office, his savannah monitor died and I went back to watch him do the necropsy. Well it turns out he stimulated the heart just by rubbing it! It freaked me out, totally! I think you did something to stimulate the heart in a way that it started beating.
Just don't beat yourself up over this. It was definately not your fault, and also your first time brumating.
Who are you callin' a freak?!