She doesn't even have to storm. She can just walk off in exasperation. Who hasn't done that? If she then failed to take a turn to go back to the RV, she would still be able to see the RV for a while walking in the wrong direction.
BTW, my daughter got to high stage 2 hyperthermia last spring in Lake Havasu. She lost consciousness. She did have a severe headache but she gets migraines, she mentioned it to no one because she hates to complain. She had vomiting, but that happened
after she was unconscious. Fortunately, her husband woke up, noticed, roused her, got her into a tepid bath (she was already back inside, thank goodness). Her temperature was just a hair under 103 (but that was after being inside for at least half an hour).
I've had hyperthermia, stage 2, myself. Was super uncomfortable at the beginning, with racing pulse, no sweat, etc. Was on I-40 at the time, following my ex-husband who was in a car with air conditioning and the kids. He ignored my signal to pull over (that was early on). As an hour went by, I became euphoric. I rolled down all the windows, began singing with the radio and waved at everyone I passed. We stopped as planned in Needles and my ex-husband (a physician) knew instantly something was wrong. He wouldn't let me drink an iced drink until I had had room temperature water (don't know if that's proper treatment - he wasn't an ER physician). We stayed in the A/C'ed McDonald's for quite a while, but I continued to feel weak and disoriented (no longer euphoric, medium headache - also common for me, unable to eat/slight nausea) so we went to a motel. I still don't think this was worth an ER visit but I do think my daughter should have gone (although...they would have done much as her husband did, just to cool her off again, but vital signs would have been taken).
So, I'm well aware that in the early stages, one merely feels uncomfortable (and I was super irritable before the euphoria set in). The effects of heat on mood were well known to Native Americans, and euphoria was one of the (desired) side effects of the Sweat Lodge.
Sweat Lodges in Drug Rehab
That's why heat is being used (as in this article) in drug rehabs.
I now know that if it's really hot and I'm starting to feel impatient, restless and irritable, I should get myself to a cooler place. Not surprisingly, our brains are designed to get us out of trouble. So Barb, already somewhat compromised by heat (Nixle says 104 out there in the mid-afternoon) may very well have gone to the RV/truck to cool off (and if my husband were deciding to take pictures, there'd have been an increase in my irritability, and I don't know about the rest of you, but I don't think as clearly when I'm irritated).
It's just one scenario to keep in mind. And it also explains the behavior of some people out on Lake Havasu or Lake Powell or especially Lake Mead, who get overheated, combine that with alcohol, and get themselves into quite a bit of trouble, doing things a sane person would probably not do.
Personally, I think RT took much longer than he thinks he did taking that photo. I also think he might have decided to relieve himself, which at his age can take a little longer. IF he is being truthful, I just think he underestimated the time he delayed and BT got lost. 
