Here's an angle I can't stop thinking about so I'll post it for the record -
To the right of Circle K when you're facing it from where MS caught on tape, there is smallish building that has a restaurant called Buns and a Pizza Hut.
In front there is a good sized shallowish parking lot. Could MS have crossed St. Landry to meet up with someone there and gotten in a car with her bike?
Maybe LE is looking for the driver of the truck only to ask them if they witnesses something like that happen. It looks like the Buns and PH aren't in the range of the camera. Also, if MS got in quietly, I don't think the gas station peeps would notice, why would they?