In the unaired 2003 pilot episode, Katara was named Kya.
The pilot was an early test episode created while Michael Dante DiMartino and Bryan Konietzko were developing Avatar: The Last Airbender. In that version, Kya is still Sokka's sister, a waterbender, and one of the central characters traveling with Aang. The character was renamed Katara before the broadcast series premiered.
According to the creators' commentary, Nickelodeon's legal department discovered that Kya was already the name of a video-game character, prompting the change. Kanna was reportedly considered as a replacement, but that name was ultimately given to Katara's grandmother, commonly called Gran-Gran.
The name Kya did not disappear from the franchise. It was later used for Katara's mother, who died protecting her daughter during a Fire Nation raid, and for Kya, one of Katara and Aang's children in The Legend of Korra. Thus, Kya is the pilot-era name for Katara, not a separate member of Team Avatar.