In The Legend of Zelda: The Wind Waker, she is a playable character, along with Link, Makar, and the King of Red Lions. In the game, it reveals that she is a sage.
During the game, she is coming into her role as an attendant to Valoo the Dragon. She also helps Link multiple times, such as at the beginning when she tries to calm Valoo down. During the part of the game when she becomes playable, you can grab onto her and she will glide for a short time. She will also be able to fly. Later in the game, she will give the sword more power to defeat Ganondorf.
"A world of tiny islands strewn across a vast sea... A girl belonging to the race of Rito used her wings and treasured harp to help the hero who traveled the Great Sea in the world of the Wind Waker. Hailing from Dragon Roost Island, Medli may be a tender-hearted and courteous attendant to the sky spirit, but she fings great courage in the face of danger. When she plays her harp, she can manipulate the very wind itself to attack enemies in a wide area. Aside from this, she can sprout her wings from her arms to attack enemies both high and low!"
"A young Rito girl who is an attendant to the Dragon Spirit, Valoo, on the island of Dragon Roost. She is kind and cheerful. When Valoo becomes enraged, she attempts to reach the dragon so that Komali can get his scale. Despite the violent winds, she refuses to give up and battles on through exhaustion."
Super Smash Bros. for Wii U
"A polite young girl from the winged Rito tribe. As the attendant to Valoo, the Sky Spirit who serves as their island's guardian deity, she's the only one able to understand the dragon's words. But one night, when Link conducts an ancient tune for her to play on the harp, she remembers another duty she must fulfill..."
As a normal villager, she will act kindly toward the player and will get along nicely with lazy, peppy, smug, snooty and normal villagers but has higher chances to conflict with cranky and uchi villagers. She will woke up around 6:00 am.