Our local paper said they went on Saturday for an overnight camping trip, so I'll assume she thought they had enough food and water for however many hours they were supposed to be out.

I'm sorry to say she made many mistakes, as has been pointed out in this thread. If I recall, they'd recently moved to Las Vegas from the east coast, so she didn't know what she was getting into. I'd guess she not only didn't know, she didn't know she didn't know, the problem of unknown unknowns.

What a disaster.