The Ending Of Netflix's Live Action Avatar: The Last Airbender Explained

Although Katara's mother Kya (Rainbow Dickerson) dies at the hands of Firebenders, Katara blames herself. Since the Fire Nation is hunting down Waterbenders like Katara, she is the whole reason the Fire Nation attacks her village. After Kya hides her daughter from the soldiers, Katara tries to use her waterbending to help her mother, but she only succeeds in catching a soldier's attention. Desperate to save her daughter, Kya claims she is the Waterbender instead, and she is killed.

Now, anytime Katara waterbends, she carries the trauma from this incident. She is afraid to waterbend, since she knows the consequences all too well. Yet at the same time, she feels that if she had only practiced her waterbending more, she could have saved her mom.

Just like Aang, who comes to realize that it's not his fault the Air Nomads died, Katara gradually accepts that she couldn't have done anything to save her mother, and embraces the sacrifice she made. Kya knew that the only way the Fire Nation would leave her tribe alone would be if they believed they had taken all the Waterbenders. She knew that her daughter was the best hope for the future, and she gave her life for that future. 

That's why Katara refuses to let Master Pakku (A Martinez) tell her to remain on the sidelines at Agna Qel'a. Katara knows this is her chance to do for the Northern Water Tribe what she couldn't do for her mother.