Breaking a stallion is rough but pretty straightforward. You fight until he concedes. A filly is more subtle.
I am no expert on horse training. But my one experience breaking a filly was educational about the difference between the sexes.
It was a lot easier to get the saddle on the filly than it had been on the stallion, she complained a bit but submitted. She let me mount her without any trouble and I was encouraged. I got her up to a walk then encouraged her to a trot. At this point I got a little resistance and had to give her a light kick. Then I pushed her to gallop and the stubbornness came out. Several times slapping the reigns barking ya and nudging with my heels was not enough. I slowly increased the pressure until she broke into a gallop. I tested her submission by guiding her in gentle turns with the reigns until I felt she was under my control. Then I let her gallop on a straightaway to see how fast she could go.
My mistake was in relaxing. As soon as she sensed that she suddenly turned right and I flew straight ahead. A definite lesson in keeping your frame.
Funny thing is I didn’t realize women do this too.