I have a friend who has a theory Opel is Lin and Tenzin's daughter which I don't understand why that would be the case. Tenzin broke up with Lin for not wanting children and she didn't seem like she was really talking to Su until Lin got to Zaofu. It doesn't blame sense for me to think that Lin gave Opel to her sister whom she wasn't talking to.
Good, I'm not the only one. Maybe I watched too much Crisis, the lead FBI (?) agent had a daughter young and let her sister raise her for the sake of her career. Much repressed emotions between the sisters and the daughter. Probably just projecting...