This wasn’t made for specifically “Barbie” but for 11 1/2 dolls in general.
I can see the potential for this to be someone’s cherished toy from the 70s. The typical fold up case style from most toys sets during the time would make this an easy play set to take anywhere.
At first I mused that Barbie would only be able to ride side saddle as her legs would not bend at the right locations. But the ad says that the horse is designed to accommodate that issue. (I am guessing that means skinny horse in the middle!)
The other thing I noticed is the way the dog is sized in the picture. If you read the ad it says the dog is 6″ tall and 10″ long. That would make the dog over half as tall as Barbie and length wise only 1 1/2″ shorter than Barbie. It would also be as half as tall as the horse and almost as long! Sneaky aren’t they…