My gut feeling is that someone is helping her, or thinks they are, by providing transportation and a place to stay.
Realistically, we're at ten days here; unless she cached a lot of supplies, including clean clothes and enough water for daily washing, and found a cave or empty house with the power still on somewhere, even at her heat tolerance, it's got to be pretty miserable. After three days backpacking in summer, I'm way past ready for a good shower, even if I'm cleaning up a couple times a day with wet wipes and/or quick water bottle showers.
It feels far more likely that she got a ride out of the area. Maybe staying with a friend in DFW or San Antonio, where she could move around freely with way less chance of being recognized. Or maybe she's just holed up somewhere not that far away, reading and birdwatching on some friend's rural property. Out of area seems to match up better with the bike coming back, though; if she's staying local and hidden, she could easily keep it with her until she's ready to return. Or maybe the undamaged bike was just her way of letting us know she didn't get run over and I'm reading too much into it.
I still can't imagine anyone with nefarious intent getting the bike back into that carport without getting caught. That does give me substantial hope that she hasn't fallen in with anyone intending her harm.
Of course, I can't say she's thinking entirely, or even mostly rationally at the moment, especially considering the obvious pain this is causing family and friends; <modsnip> The big problem with an irrational thought process is that it's extremely hard for reasonable people to follow, and pretty much by definition, impossible to predict. At this point, all we can really do is keep reaching out to friends and acquaintances, hoping and praying that either someone will find her, or whoever is helping her will talk her into coming home.