I know that people upthread were griping about comparisons to other cases, but I can't help it. There is another active case on here of a young woman last seen leaving work. One theory is that an acquaintance of hers asked her for a ride from her workplace.
I wonder if something like that happened. When Allison ran out to her car for whatever reason, someone she knew was out there too. I'll call the unknown person N, like someone did above.
N: Hey, Allison. I need a ride to ____. Can you help me out?
A: (Being the nice girl she is.) Well, I am on my break so...
N: Oh please? I have an appointment, have to take my kid to the doctor, etc. You can just drop me off and come right back, You're the boss! LOL
A: Well, ok. I have to stop and get gas though.
N: That's ok, oh man, I sure do appreciate this. I owe you one!
She may have left voluntarily with this person, thinking that she was doing a good deed (I am always in that mindset, though I shouldn't be). Figured she could make it quick, and well, she did need to get gas. So, she wasn't under their power knowingly at the gas station. No frightened look, no clues to the cashier, etc. But perhaps did look a little "on a mission" because she was maybe bending the rules a bit.
When she got in the car, or sometime thereafter, things went downhill fast.
Why didn't she take her purse, phone, etc. ? Because she hadn't planned on leaving the premises.
Not saying this is what happened, but IMO it is surely possible.