BR Cocks attacking 1 poor Silver Laced Wyandotte

[Owner of Elvis]

OK...I have 3 -26 week old Barred Rock Cockrels. They are really gentle and quite tame. They have begun to seek out and try to mate with a 17 week old Silver Laced Wyandotte. They have BR two females with which they "hook up" but they seem to enjoy tormenting the poor little SLW. She hides in the coop most all day and when she comes out they immediately go after her. Poor thing flew into the garden to escape them last night. There are 12 other pullets of which they show no interest in. Any ideas?