George's sister

3rd Grade Female Moose is the sister of George Lundgren. She appears in Sue Ellen's Little Sister racing with George in the Brother and Sister Race at the Annual Picnic.

After that appearance, she received a cameo in the special Arthur's Perfect Christmas where she was dancing with the rest of her family. Aside from this, this character has yet to make a return appearance other than a cameo.

She has made cameos in several episodes, like in Muffy's New Best Friend when she is seen on a ride with George and in Bitzi's Beau she is seen walking out of Lakewood Elementary School.

She made her last appearance in the special Arthur's Perfect Christmas and has never been seen since.

Appearance
3rd Grade Female Moose has skin complexion a little lighter then her brother.She has auburn dark colored hair with bows in them. She wears a red short-sleeved shirt with a white shirt under it, and wears denim shorts.

Trivia

 * It's possible this character was going to be used as part of George's family, but apparently never materialized and she was eventually written out of the show from what we have seen due to her lack of appearances in episodes after Season 5. Especially after Arthur's Perfect Christmas, which was her last appearance.
 * Although she is George's sister, she is never seen in his household other than Arthur's Perfect Christmas.