It has been for-told that Aang was not an only child. But that a young girl, a twin, was born with him. In the womb of their mother, the powerful spirit Ravaa didn't know which child to choose. They were both strong and determined. So she placed a small amount of her spirit in the girl and she put herself into the boy. The small spirit in the girl gave her the ability to bend all of the elements but the girl was never allowed to go into avatar state. When born the children grew up with each other a small time. Then Aang chose the toys of which the avatar chooses. And the young girl was sent back to her parents..... But what exactly happened to her? Did she ever meet her brother? Does she ever proceed her talents?
I only own Kyra and her children the other characters are owned by the makers of ATLA and TLOK.