It all makes since now.
You said "someone had stuck a gun to her back".
Just because there is a gun stuck to her back, that doesn't mean that someone stuck it there, alright? Things don't have to be so violent, mmk?
So based off exactly what you said, maybe she picked up her husband who works at the shooting range. For easy access to weapons they usually velcro their guns to the walls.
So she was wating for him, and rested her back on the wall.
She may have forgotten that her shirt had thick fabric. And the gun stuck to her back, hence she "had stuck a gun to her back".