Would it helped if she was drugged and totally strapped down and gaged on a breedingbench?
She would die and this conversation would be used as evidence in your murder trial. Both breeding bench and belly riding are fantasies promoted by people that have never touched a real horse.
In a different thread around here, another horse experienced member and I talked about "going in after a foal". Baby horses are half of mama's height at birth. They have to be to reach the teats. They have to unroll and twist in a very specific fashion to be birthed. If anything goes wrong, both die. I have been shoulder deep in a mare's vagina with my cheek hard against her hip trying to reach the foal's feet to guide them out correctly. That's why the phrase "hung like a horse" has meaning. A stallion needs that much penis to do the job.
When a stallion mounts and thrusts, he expects that much vagina in front of him and like males of every species, he is going to try to give his sperm as much of a head start as he can. A human only has two possible ways to withstand that kind of assault, either choose a horse smaller than yourself (then you wouldn't need a bench) or roll with the punch. Believe me, with muscles capable of launching the weight of a small car over a six foot fence behind it, it's a serious punch.
The reason you see men taking horses but not women is because the shape of the male pelvis and location of the anus make it difficult for the horse penetrate through the pelvis. You have to angle your body just so or the impact of the horse's penis on bone and just pushes you around. Vaginas, on the other hand, align nicely with the larger pelvic opening in women. There's nothing to stop the horse from penetrating all the way through to her lungs but a little stretchy tissue and her reflexes. That's why when you see the ultra rare vid of a woman taking a full sized horse vaginally, she usually screams and runs away when the stallion thrusts. Even the women taking minis will grunt and flinch at the impact.
That's why I strongly suggest going to pure fantasy route.
Thanks to thebestguy for letting me post this