Shelly is one of the three Aqua Admins in Team Aqua. She appears in the Generation III games. She has long, curly ginger colored hair. Shelly wears a blue bandana similar to May's.
Shelly is a very strong trainer. In Sapphire and Emerald she appears first at the weather institute and then at the Seafloor Cavern. In your first battle against her, she has a Carvanha and a Mightyena. At the Seafloor Cavern the only change is that her Carvanha has evolved into Sharpedo. Shelly doesn't appear in Pokémon Ruby.
In the anime Shelly has a Carvanha but instead of a Mightyena she has a Walrein and a Crawdaunt.