Sometimes girls will wear something that they can then remove later, i.e. an overshirt of some sort over a barely there camisole top. When they leave the house, they toss the more modest dress for the slut puppy look. The only way to avoid this is to go with the girls when they shop for clothes and let them know what's acceptable, and what's not. It doesn't help that almost everything marketed to pre-teens and teens these days is 'ho' fashion.
The other defense as the mom of sons has been to talk candidly to them and refuse to condone something that isn't acceptable.
"What do you think Grama would say?"