“I got the eye of the tiger, a fighter, dancing through the fire
Cause I am a champion and you’re gonna hear me roar
Louder, louder than a lion”

Katy Perry – Roar Lyrics on LyricsMode
She is like a tiger fighting others without any care because I am a champion and you will hear me scream louder than a lion can do.
It means she is not afraid to do anything she want to.