Other mistake: When Elizabeth's horse takes the bad fall, Maryellen tells them it has a broken hoof. So they put the horse down instead of taking it to a nearby vet for help.
Suggested correction: This episode takes place in 1945. We see Mary Ellen look toward the mare's front (not hind) legs/joints, which are weight bearing; and when Mary Ellen tells Elizabeth about her mare, Molly, Mary Ellen's actual words are, "Elizabeth, it's her leg. It's broken. It's bad. We're gonna have to put her out of her misery." Viewers are not shown what Molly's "bad" break is, but with Mary Ellen's words, we know the break is severe, which was a death sentence for any horse. Just to add, it all completely depends on the location of the equine injury and the severity of the break/fracture. Nowadays, with modern advancements in equine veterinary care, (thankfully!) some severe breaks may not be a death sentence for a horse.