This model was originally sculpted by Carol Williams. You can see more of her work at her website: http://www.riorondo.com.
The Ideal Stock Horse (ISH) mold was finished in 1999, and as you can see, on many of the models today, that original date is still marked underneath the back legs. The first edition model was called Pretty Consecutive in 1999. You can see more pictures here: http://www.stonehorseref.com/Horseinfo.aspx?HorseID=84.
The ISH was the first model that had mix and match manes and tails; there was a long and short mane, and a long and short tail that could be interchanged to create new looks for the mold.