Sadly, I don't have any photos of this horse--she left my life years ago--but I just remembered her the other day and now it's bothering me that I can't find evidence of her ever existing!
She was a large purple horse--think Barbie-sized--with a speaker in her belly that made rather loud whinnying noises. Her legs definitely had some measure of poseability; I distinctly remember ankle and knee joints at the very least. I believe she had plastic of some kind (dots, maybe?) where her mane met her head, and if I'm remembering right her mane was either white or blonde with tinsel.
This had to have been released in the early '90s to early '00s sometime, as that's when I remember having her. I've always lived in Canada if that helps.
I've already crossed out the Starlight Walking Horse for sure, as she never had a remote control.
Thanks for the help!
EDIT: Now that I'm thinking about it, it's also possible her hair may have been pink. In addition, she had no fantasy parts (horn, wings, etc) and I distinctly remember that her speaker was rounded and indented slightly. I also used to put these velcro stars in her hair, though those may not be related.