A dog crate or wire crate would be fine. Or extra crate you can make with wire. Someplace where she can have access to her own food and water and a bit of shelter. It doesn't have to be that big. The fact that they ignore her might mean she's already at the bottom of the pecking order. Give them something to do, or play, or scratch at. They might be bored. Boredom often leads to hens pecking at each other, and the one lowest in the pecking order is usually the first to get it. Try giving them a head of lettuce on a string or throw some treats in the run area for them to hunt and scratch for.