Dear Lin,
I know we haven't spoken since I left Republic City, but I wanted to say that I'm sorry for everything. You were right, and I was being completely irresponsible. You were just doing your job and rightfully so. I miss you so much.
Living with Grandma and Grandpa was fine, but I just felt out of place there. I didn't feel like I belonged there, so I left. I joined this crew I met on a pirate ship which was fun for a while, but I still didn't feel like it was where I needed to be. Since then, I've joined this amazing traveling circus. I know it sounds crazy and kind of stupid, but I really love it. Everyone is so nice, and I'm learning so much. There's a kid here from the Southern Water Tribe who is so funny. I think we're going to become good friends.
Maybe one day I can visit you and Mom in the city. I'd love to see you. Or maybe you can come visit me sometime. Whichever works for you.
I love you, big sis. I really am sorry and hope you'll forgive me. Write back when you can.
Love, Su
Yes, the kid from the water tribe is supposed to be Varrick. It's canon that they were both in the circus at some point and I love the headcanon that it's where they met.