There's many potential reasons. Personally, if he's representing a potential threat to her life I'd get rid of him, not her, because it's unreasonable to have a flock that runs its own cull program, lol! That's MY job, not theirs. It starts with one, but if you get rid of the victim, not the bully, the bully only chooses another victim. It's what they do. No matter the 'reason' for the attacks, it will continue as long as you keep the attacker. There's always reasons to attack, if one has that mentality.
Get rid of animals that harm others and the trait doesn't breed on and soon enough you can have all the chickens you want, minus the damages. I can safely leave wounded and ill chickens among the flock because I got rid of cannibals, killers, and bullies. It's very peaceful and I have many roosters and hens together without violence... Highly recommend no tolerance to bullies/harmful animals.
Anyway. Some possible reasons (but not necessarily justifications):
>She's physically sick.
>Her hormones are imbalanced, causing him to perceive her as a male.
>Her health is superior to the other hens, giving her a redder crest/face/wattles, which he is perceiving as masculine.
>She's broody or almost-broody, which can trigger abuse from less instinctive animals that don't understand it.
>She's mentally unwell, perhaps toxified and acting strange.
>She has bad genetics.
>He's physically or mentally unwell.
>His hormones are imbalanced.
>He's got enough instincts to know it's his job to find food, nests etc, and knows he can't support so many hens.
>He perceives the area to be overcrowded.
>He's used to only a certain breed or type of hen and she's not it.
>He's confused about gender roles due to lack of exposure to other males or normal family structure.
Sometimes it's just diet that makes this happen. If they're not getting everything they need, this seems to trigger an instinct to depopulate, as less animals means more nutrition to go around.
Also, this is a good example of the reason why 'x' amount of hens won't stop a violent rooster being violent. Throwing more hens at a bad rooster is a waste of hens.
Best wishes.
