Oh, dear. What folly it seems to me to keep young women in such extreme ignorance until right before they get married. Not that I think Sarah's much more informed now than she was before. What dreadful ideas she must have, having only once glimpsed horses mating! If you told them when they were younger they would have time to get used to the idea and not be freaked out by it; furthermore, they would be better prepared to guard themselves against young men who want to take advantage of them.
I don't think George will mind waiting. He doesn't seem like he's attracted to Sarah at this point, just because she looks so young, and he'd probably prefer to give her a couple of years to mature first.