I thought I read that the girls went to another address before taking the jeans to the AN Store (I'll have to look into that). Anyway, this store is the only anchor in the whole shopping story. As I understand it, a Lay Away was used to reserve (merchandise) for future delivery, while payments were in progress.
https://www.collinsdictionary.com/dictionary/english/lay-away (US)
Which means Renee had been in this store before (maybe 2 times or more). At least once to order.
This store, I don't know if it had closing hours for lunch, but Fort Worth residents should know. Plus, before Christmas, there must have been other customers. However, when you read the story, you get the idea of two (or three) girls alone in this large store located at an important crossroads.
Maybe with little Julie Ann alone in the big car in a deserted parking lot like in a movie (missing the nightfall).
However, it was the middle of the day, before Christmas, and during the school vacations.
What may have happened was that Renee had been talking to people about the jeans she was going to get...
What may have happened was that Renee was spotted by a guy who was there for boots or something, and saw the girl go into the fitting room. Probably "man and woman".
It could have been someone who knew one of the girls (or not).
He could then have followed the girls with his car, honked the horn, they could have pulled off to the side towards SS. (Although there are two routes, but we don't even know if Rachel liked driving on the Freeway or not).
Theories which, 50 years later, lead nowhere, but which could have been exploited at the time.