This is a fakie Barbie-size horse (10.5″ tall) that came with a fakie Frozen Elsa doll. I bought mine new from an eBay seller and it came in a plain cardboard box, like mail order catalog items sometimes come, so maybe it was a catalog item originally. It is a regular pony, but comes with a detachable unicorn horn headpiece.
Here is a translucent pink version of the horse. It was sold with a “Gem Girls Fairy Angel” by Midwood Brands.
This is a pink version found in the wild:
