We were asked that same question sixty years ago when we came back from visiting Juarez.
We’ve been asked it every time we came back over the years.
This is not about crossing the border.
She was not crossing the border. The Border Patrol has checkpoints which have permanent structures on various roads leading out of El Paso. There is such a checkpoint on the westbound I-10 somewhere near Las Cruces, NM, and a checkpoint on the eastbound I-10 near Sierra Blanca, TX.
A few years ago I flew into ELP airport and rented a car to drive up to the races at Ruidoso Downs, NM. I had to stop at a Border Patrol checkpoint near the TX-NM border south of Alamagordo. The uniformed agent looked surprised when I told him I was on my way to the races.
It is a little troubling when you are obligated to answer a policeman’s questions as to where you are going when you have not crossed a border and there is no probable cause for a policeman to have to speak to you. However, I do respect the work of the Border Patrol and the fact that it is extremely thankless.