[EDITED: Sorry y'all. I'm going to leave this post here in case it's not completely crazy, but I just realized how absurd it might be for a mountain lion to take a grown woman. I've been reading about this possibility in Jaryd Atadero's case, but he is a child.]
I think it's a plausible theory but I think there would at least be drag marks.
Just had a thought. I know nothing about the desert, but aren't there mountain lions out there? Unfortunately, if so, that would probably be my #1 guess as to what happened to Barbara, and would be something along the lines of what her husband is thinking (abduction). I have read that they can carry off large prey with no trace whatsoever. I sure hope I'm wrong and she shows up unharmed today.