In horror contexts, a "Pony Girl" typically refers to a human (usually female, but not exclusively) who is forced or conditioned to behave like a show pony or draft horse. This involves:
The horror derives not from gore but from erosion of identity and the grotesque submission of human will. XXX-COMICS - dofantasy - Pony Girl Horror
Horses occupy a liminal space in Western psychology: noble beasts, symbols of freedom, but also broken animals (gelded, saddled, whipped into submission). The Pony Girl literalizes this brokenness on the human form. Horror exploits the “uncanny valley” between human woman and horse—too much anatomy shared, too much dignity stripped. Title: "Moonlit Terror: A Pony Girl Horror Story" 1