There was this, I don't know if it was a cartoon special or an actual show but it started with a girl, who was from another world, being left on the doorstep of a couple from our world, and it had a black horse... I'm pretty sure it's not Lady Lovely Locks but I can't remember what it was called... I.She had to eventually go back to the other world too. Does this sound familiar to anyone? Lol She did have blonde hair though.. It came on Cartoon Network around 1993-1994. If I could just find the intro, I know I'd remember what it was because all that happened in the intro.

Maybe,.

Wildfire (86)

The queen of a magical kingdom has her friend a magical horse named Wildfire take her newborn daughter away to Earth to keep her safe from the clutches of an evil sorceress. Her mother left her baby with an amulet with the insignia of a stallion on it. She grew up on a ranch without suspecting her royal heritage in the other world. When she became of age, the amulet summoned Wildfire to bring her back to her mother's magical realm

-Watch Opening-
Wildfire

-Watch-
YouTube - Wildfire Ep 1 Once And Future Queen Part 1