This  is Rainbow Flash, she's one of the Super Long Hair Ponies released in Year 2 of the pony line. Rainbow Flash was originally sold alone but was later sold with a baby pony named Baby Romperooni.

Rainbow Flash has a shimmery pink body and rainbow-colored eyes with a blue heart. Her mane is orange, pink, purple and yellow, and her tail is pink and purple. Her symbol is a yellow sun peeking out from behind a white cloud and a rainbow arching over the top. She has a light green hoof heart on her front left hoof and a magnet on the bottom of that hoof.

As one of the Super Long Hair Ponies, Rainbow Flash's hair is much longer than usual. Her mane has gotten frizzy, especially towards the ends, but her tail is smooth and silky and her body is in good condition. 

The bottom of her foot is marked "2002 Hasbro."