for the most part, he isn’t outright aggressive to anyone else other than her. he’d do a lot of bluff charges but that’s about it. honestly, i think that’s what he did to her when she hit him. i was talking to my mom last night about it again and she said she panicked because he ran at her and she just started swinging.
when he tries to bluff you, he just runs at you and stops before he gets close. i think that’s what he was doing and she thought he was trying to full on attack her. idk, she did say she’s terrified of roosters and i think they pick up on that.
i thought he has/had a concussion because he can still move his neck and it isn’t limp. he’s just keeping it tucked/scrunched in.
He had me help him care for the little peepers and I became very attached. One of them did try to come for me one time. 
She jumped and flew at my face trying to grab me with her feet. I had to hold back the urge to smack her away. It was very scary. But once I got a hold of her and submitted her she was calm. Now she is the most submissive bird in the flock. I think your mother would do well to, if not learn to submit the birds herself, at least watch some behavioral videos so she knows when she is in real danger so this doesn't happen again. Im happy she is at least trying to help him.
