Where to find selphy on FireRed?

In Pokémon FireRed, Selphy, also known as the "Sevii Islands' trainer," can be found on Seven Island, specifically at the Resort Gorgeous. You need to access the area after completing the main storyline and obtaining the National Pokédex. Look for her in the hotel where you can also participate in various activities and battles. She will challenge you to a battle, and defeating her is part of the game's post-E4 content.