I'm not sure exactly what is going on with the new hen. Do you have her in the coop and run with the others? How long has she been there?
If she has been in the coop and run for about a week, she should return to the coop and run at bedtime. She may not want to go in the coop with the others if she is truly being picked on real bad, but she should want to and at least go in the run.
If she has not been in the coop and run for at least a week, can you keep her in a cage, dog crate, or something, in the coop where the others can't pick on her? After a week in the coop in that cage, she should figure that the coop is home and want to return there at night.
Once she accepts that the coop is her home, it would be real good to free range them all. There are two different kinds of aggression when you integrate chickens. The first is the pure integration. That is where the other chickens accept her as a member of the flock. If she is not accepted, she is a stranger and a threat. If she tries to hang around with them, they will try to run her off. Once they recognize her as a member of the flock, they quit going after her.
The other type of aggression is the pecking order. It sounds like she is younger than the others. If she is still less mature than the others, then she will be at the bottom of the pecking order. That means that if she invades the private space of another chicken, the chicken higher in the pecking order is within her rights to peck the chicken lower in the pecking order. They don't always enforce those pecking order rights, especially if the pecking order is firmly established, but sometimes they do. What usually happens is that the chicken lower in the pecking order runs away and it is over. So a hen clearly lower in the pecking order is wise to avoid the other older hens. That is why a bunch of chicks that have been weaned by a broody and are fully integrated in the flock still hang out away from the rest of the older chickens until they grow up and mature. Then they can find their place in the pecking order.
With all this, once your hen accepts the coop as her home, free ranging them is a good idea. That gives her a better chance to stay away from the older hens until she has matured enough to really join the flock. But expect her to sort of hang on the outskirts of the flock for a while.
If she has been in the coop and run for about a week, she should return to the coop and run at bedtime. She may not want to go in the coop with the others if she is truly being picked on real bad, but she should want to and at least go in the run.
If she has not been in the coop and run for at least a week, can you keep her in a cage, dog crate, or something, in the coop where the others can't pick on her? After a week in the coop in that cage, she should figure that the coop is home and want to return there at night.
Once she accepts that the coop is her home, it would be real good to free range them all. There are two different kinds of aggression when you integrate chickens. The first is the pure integration. That is where the other chickens accept her as a member of the flock. If she is not accepted, she is a stranger and a threat. If she tries to hang around with them, they will try to run her off. Once they recognize her as a member of the flock, they quit going after her.
The other type of aggression is the pecking order. It sounds like she is younger than the others. If she is still less mature than the others, then she will be at the bottom of the pecking order. That means that if she invades the private space of another chicken, the chicken higher in the pecking order is within her rights to peck the chicken lower in the pecking order. They don't always enforce those pecking order rights, especially if the pecking order is firmly established, but sometimes they do. What usually happens is that the chicken lower in the pecking order runs away and it is over. So a hen clearly lower in the pecking order is wise to avoid the other older hens. That is why a bunch of chicks that have been weaned by a broody and are fully integrated in the flock still hang out away from the rest of the older chickens until they grow up and mature. Then they can find their place in the pecking order.
With all this, once your hen accepts the coop as her home, free ranging them is a good idea. That gives her a better chance to stay away from the older hens until she has matured enough to really join the flock. But expect her to sort of hang on the outskirts of the flock for a while.
