Someone has suggested, tongue in cheek, that the head covering may have a similar magical quality as that found in Sampson's hair--that is, one is powerless to abuse a girl so long as she remains covered, but if he can in any way get the covering off her, she's fair game. I don't think that theory will hold any water in Linda's case. She appears to have come under Justo Smoker's power while still fully dressed in her church outfit.
The magical piece of cloth just isn't working.
UPDATE AUGUST 24: More information has been disclosed in both of these kidnapping cases. It turns out that Sasha Krause was tied up and beaten, then shot in the head--and both her underwear and her head covering removed and kept as trophies--but the autopsy indicates she died a virgin. That must be some comfort to her family--and may even strengthen their belief in the magic piece of cloth. In Linda Stoltzfoos' case, she has not been recovered, but some of her underclothing was found buried in the woods--indicating that she could have been raped; there was no sign of her head covering.