I am usually just a take their word for it kind of person on stuff like this and am glad she's ok, but it still seems strange.
First, no phone? If she is an avid hiker, that's hiking 101 - you get cell service almost anywhere on federal lands now. I was in the BFE back country of the GW National Forest the other day and had two bars, let alone a day hike from the valley at zion.
If she started from the grotto, you would have to make an effort to find a place that no one would see you for 12 days.
12 days with no food presumably, which is doable with adequate water, but apparently she didn't have that if she is severely dehydrated.
Temperatures ranged from 40 to 90 and she survived that exposure for two weeks with likely very limited Clothing supplies on a day trip.
Maybe I'll be proven wrong and am fine if I am. But it still seems weird. But again, the important thing is she's ok.