My only addition to all above advice is to check that hen over really well.   We recently had a similar issue:  rooster chased/attacked only one hen, but that hen was not bullied by anyone else.  I don’t think he was drawing blood though-at least never witnessed that, but witnessed the aggression plenty of times.  Even when we put her in a cage in the run, with food and water for a few days to allow her some peace and to eat/drink, rooster would come over with flared neck feathers and try to attack -similar to what 2 roosters would go (but the hen was actually a hen, and was trying to get away).   In the end, it turned out the hen was sick- she had done kind of infection on her vent area/lower belly, and started to separate herself from the flock and was acting different.  We had to remove her bc it was pretty bad (she passed away later).  So, I think he was keeping her from the flock bc she was ill.  Birds hide any illness/weakness by nature bc they are prey animals.  So when we (the humans) notice, they are usually pretty sick.  The flock notices first - and often bully or keep away sick birds.