Kid Kore made Barbie fakies in the 90’s, some of which came with horses. Jodi dolls had a series called Shenandoah Riding Club. The ponies are about 5″ tall:
This is a larger horse, 7.5″ tall. I’m not sure if this was for Katie or Kelsey dolls (Jodi’s sisters), or from Kid Kore’s more Breyer-esque line Stable Champions:
