Katara has changed a lot since the events of Avatar: The Last Airbender. She had married Aang and outlived him for many years. Their children are Bumi, Kya, and Tenzin.
We mainly see her interact as a grandmother and mother. I was a little surprised she didn’t live with Tenzin and his family. I know she’s not an Airbender, but it would make sense.
She does provide some healing for various characters including Korra, but she doesn’t fight nor is she really that important to the story. But I was glad to see her return.