Answer:
Katniss is the mockingjay- literally she isn't a bird, but she is the thing that survived despite the Capitols intentions, like a mockinjay.
Katniss, the Girl on Fire- She is the spark that set the districts alight with the idea of rebellion and the courage to change. She's never actually on fire... except for that bit where she gets hit with a fire ball in the Games... but other than that, it's a metaphor
No. Katniss was called the girl on fire because...............................................they lit her up in the introduction? Have you even read the book? UmmNo! So?