Ty Lee, one of seven identical sisters, was born to Fire Nation nobility. However, it's possible that there was at least one Air Nomad in her ancestry. Redditor u/Juxitr assembled a slew of evidence in favor of this theory, starting with Ty Lee's appearance: She's got the gray eyes and brown hair characteristic of the Air Nomads.
The animators of Avatar took great care in crafting their world, and use appearances to indicate nationality. People of the Fire Nation have gold eyes and black hair, waterbenders and earthbenders have blue and green eyes, respectively, and Air Nomads have gray eyes. Ty Lee doesn't look like Azula, Zuko, or Mai in this regard, but combined her round face and constant smile make her look a lot like Aang.
The spinoff series The Legend of Korra gave us several more Air Nomads to compare with Ty Lee. In fact, Aang's granddaughter Jinora somehow strengthens and weakens the Ty Lee theory at the same time. The two look like sisters, but curiously Jinora has brown eyes. Her airbending siblings and father all have gray eyes, making her a mysterious outlier of the family.
