I don't have any proof that girls with Asperger Syndrome love horses any more than typical girls do, but I have my suspicions. Asperger girls often love animals, and by the age of 8 or 9, many do seem to gravitate towards horses. And in many ways horses are an ideal interest for a girl with Asperger's. The one-on-one relationship between a girl and a horse is rewarding and calming, and an obsession with horses is a socially acceptable, even expected, passion for girls in general. There are stables in just about every town where girls can be taught the specific rules of grooming, tacking up, and riding a horse. Often there are group riding lessons, where the Asperger girl can be included with a group of like-minded and same-age peers as they all learn to ride together. This set-up works well for someone who struggles socially, because each child is on a horse, working individually, and being supervised by an instructor. The social pressure is much less than in, say, soccer or gymnastics. An added bonus is the possibility of making a friend during the brief social period before or after the lesson, and girls with Asperger Syndrome do well when they have a good friend with a common obsessive interest. Once a girl is knee-deep in the world of horses, all kinds of possibilities open up. Summer camps that revolve around riding, for example, or Pony Club and 4H.
Since many typical girls love horses, the Asperger girl's involvement in the horse world allows her to fit in with peers she might otherwise never have met. It's not perfect, of course. There are just as many mean girls at stables as there are in school. But where an Asperger girl may feel left out of the social world at school--boys, makeup, celebrity gossip--she will fit right in with the girls who want to talk about horses all day.
If you have a daughter with Asperger Syndrome showing an interest in horses, I encourage you to ask around to find a good local stable where she can begin to learn everything she wants to know about horse care and riding. This is something that may bring her joy, fun, and friendship for a lifetime.