So was the mother hen never separated from the flock; the chicks were all raised with the flock instead of an integration process? She might be taking more after the Orpington, personality wise. Orpingtons tend to be more docile, thus risking being lower in the pecking order. Size doesn't always matter when there’s an aggressive small hen. (I've had bantams bully my Orpingtons before!)
From what I can see of her saddle, it looks like it was made out of strong materials. Again, I highly recommend trimming your rooster's spurs and nails down.