Contributed by Ginger:
Jin was introduced into the show in the 2.15 episode, "Tales of Ba Sing Se". She lives in the lower ring of Ba Sing Se, and was a frequent customer at the teashop where Prince Zuko and Uncle Iroh worked. At first, Zuko thought that Jin was suspicious of him and his Uncle and their hidden firebender status. In reality it was quite the opposite -- Jin had a crush on Zuko! She asked him out, and Zuko was left with a baffled expression on his face while his Uncle told Jin that Li (Zuko's alias) would love to.
We see from their date that Jin is a fun-loving girl. She was easily pleased by the fact that Zuko "was in a traveling circus", and wasn't at all discouraged when he couldn't juggle. She was optimistic and kind, even when the date got painfully awkward. She always seemed to generate a genuine, kind aura. She became excited over the simple things in life, like the Firelight Fountain. A war is raging, but she and the other citizens of Ba Sing Se can't talk about it. Some were scared and unhappy, but Jin was carefree and joyous.
There was an instance where Jin might have realized that Zuko was a firebender. When they reached the Firelight Fountain area, none of the lanterns were lit. Zuko, seeing Jin's disappointment, asked her to close her eyes and he lit all of the candles so quickly; it would have been extremely difficult to do had he not been a firebender. Jin was surprised to see them all lit, but didn't seem overly suspicious of how Zuko did it, and was content without knowing his method.
Soon after Jin tried to kiss Zuko, but was stopped when Zuko gave her a coupon for a free cup of tea. After thanking him for the gift from Uncle, she kissed Zuko. He started to return the kiss, but quickly backed away. Asking what was wrong, Zuko said it was complicated and left.
Jin hasn't been seen since, and it's not known if she used that tea coupon before Zuko & Iroh moved higher into Ba Sing Se.