I realize I don't know you or your wife, so I won't try to psychoanylize her reluctance to carry. I do strongly question an employer who will assign a person to go into a potentially dangerous situation wearing the clothing you describe. Would you go into a potentially dangerous situation, wearing only a tank top, swim trunks, and flip-flops? No way to run, or fight, and no way to move away and blend in. If she is going to be INSIDE a van, then at the least she needs to be wearing socks and running shoes. If she is minimizing the clothing due to the heat, wearing shoes won't affect things that badly. Heck, she could even wear those strappy sandals that are made for hiking, etc. If she STAYS in the van, she can bring the arm in a gun bag, and just let it sit on the shelf, since inside the van means just that.
If the mode of dress is firm, then that sounds like she is being made a target, and is going to be outside the van. In that case, wherre is her commo? How is she hiding her radio?
this sounds just a little weak, from the standpoint of the employer.