Katniss is the main character in Catching Fire because the story is from her point of view. She is also the main character from the first book of The Hunger Games series, making her the main character of the whole series.
Other reasons why Katniss is the main character include:
The main character
Yes
The protagonist is Katniss Everdeen. She is the first-person story teller and the main character of the series.
Yes. Catching Fire is written from the narrative perspective of the main character, Katniss.
Katniss does not find out in Catching fire, but in the first book, when they are in the cave by the river.
No.
no they do not
Peeta
No, but she does in Mockingjay.
Katniss does what Haymitch does
Still Katniss Everdeen.
**This answer will contain spoilers! Don't read unless you're not planning on reading Hunger Games, Catching Fire, or Mockingjay!**Throughout the story Katniss is never "with" Peeta, it is mostly an act. In Catching Fire, Peeta stages a proposal for the capitol and she says yes, but later they break this off because they're busy escaping from the capitol.