She seems like she's definitely a dominant hen in general, but she's overcompensating for not being where she wants in the order. Maternal doesn't necessarily mean she has to treat others kindly. I have some very mean maternal hens lol. They make great mom's to their babies but treat everyone else younger like trash.
She sounds to me like she's trying to either get a spot in the pecking order or trying to keep her spot (especially with the roosters passing). The hurting of the leg is not good and a sign of over aggressiveness in general. In all seriousness, that's a fight that has gone to far. Which could lend more into the rooster hen aspect. My Andalusian roohen was a monster hen for awhile, her name was Flapjack before, but now she's called Jail Bird because of all the separation I had to do. You may need to eventually break up the pecking order if this keeps up for awhile or gets worse. Jail Bird has turned her life around she is very happy now and hurts no one. You can fix this with time and patience. Either way you'll need to keep a close eye on her. She could kill another hen at this rate.
The Orpington may well be the leader though. My Australorp, Kira, is definitely the leader in her flock. Pretty much the same attitude as your Orpington. She was my first chicken. When my precious Faiyumi, Jadzia, was still around, they had a wonderful dynamic. Jadzia would run to Kira, Kira would then give Jadzia an order (it was very clear she was eyeing the chicken she wanted pecked). Jadzia would then run off and enforce the pecking order on that chicken. Kira herself never pecked anyone and never got pecked.
So my guess is your Orpington is top hen too. They all sound adorable and like a fun dynamic. I love mixed breed flocks and exciting interactions they have with each other.