Very sorry to hear that....
CO is an especially tricky hazard, you can think that you have taken proper precautions and still have a tragedy occur...
One such case I read about long ago was a man that for some reason felt he needed to leave his car running in his garage... he thought the garage was properly ventilated, and maybe the garage was... CO is lighter than air, it rose up into the upstairs bedroom and killed his wife while she slept.
It doesn't take stupidity, it just takes a moment's inattention- and in the aftermath of a hurricane I would imagine its easy to get distracted.