She was a bounty hunter who goes to planets to capture species. She only appeared in the episode "Zoobotnik." One of the first things that she does is kidnapping the Mobian citizens (Tails included). Also in the episode, she falls madly in love with Dr. Robotnik, and agrees to help him capture his arch nemesis Sonic just as long as he marries her. They use a fake Tails doll as bait. Since Sonic knew that there was no chili dog breath on the doll, and he never talked when water was in his mouth, he plays around and pretends to be captured.
After he'd been captured, Katella wanted to marry Robotnik (much to his displeasure) and Sonic poses as the parson and instantly weds them. However, he had earlier called Mama Robotnik about the wedding, and she starts to fight her. After this, she calls the marrriage off and leaves Mobius while chasing after a moustached planet.