Yes, from this thread we've learned that many people DO go hiking in the desert in July wearing bikinis, etc. That is important information, in my mind. Moreso, that Barbara's family doesn't think it odd. That being said, other posters have pointed out that voluntarily going off the beaten path (literally) would likely result in much discomfort, as the area is rife with nasty prickly-type things. In trying to put together a likely scenario, it doesn't seem likely, at least to me, that Barbara wandered off the path voluntarily.
And, regarding the search. There are many times when searches don't initially find the lost person and then do so on the second look. However, I just wouldn't expect that in this case. This isn't a situation where someone went off hiking and their loved-one became concerned after he didn't show up after a few days, or the person was last seen at the trail head, setting out on a 10 mile hike. Barbara disappeared in a few minutes! Her husband searched within at least an hour of finding her missing, I believe, and the "official" search was robust, early in the disappearance, and had a known location, vs. "she was going to go hiking the abcde trail in the xyz national park". She had no supplies (water) and little defense from the elements. She has to be around pretty close to the last sighting, methinks, if all is as we've been told.
This is very odd to me, especially since they apparently found no trace of her. No hat. No beer can (mug -whatever it was). No trace.
There are always the unlikely-but-possible theories, such as abduction; voluntarily leaving, then something untoward happening afterward; animal attack, etc., but there being no evidence of such one really wonders.
We've also been offered no medical history, such as diabetes, dementia, etc. I'm beginning to think that Barbara isn't there. Was she ever? Not sure, but putting all the available information together, I'm starting to wonder.