Here are some of the non-UK Jill editions I’ve found over the years. It’s not always easy to identify which Jill book is which, as titles often don’t bear a lot of resemblance to the originals. One of the Spanish titles, for example, is Jill y el Caballo Loco, which translates as Jill and the Wild Horse. So presumably not Jill and the Perfect Pony. I don’t have a copy of the Spanish version, so I’d guess they might mean Blue Smoke in Rosettes for Jill. Or they might mean Rapide when Jill first gets him (though he’s not exactly wild …).
If you have any other editions I don’t have here, I’d love to hear from you.
There were at least two Jill editions published in the United States: Gymkhana, which became A Horse of Her Own, gymkhanas not being much of a thing in the States, and A Stable For Jill, which was much the same as the original.