Yee-Li is a young girl (probably 12) from Ba Sing Se who has a crush (though not as crippling as Won-Yee's crush) on Avatar Aang.  She and her friends are members of -- indeed are "co-presidents and co-founders" of -- The Ba Sing Se Chapter of the Avatar Aang Fan Club.  We can assume that Yee-Li has rich parents, since she was able to buy an Air Nomad flute (probably a rare item) "a couple of years ago" -- when she was likely ten years old.  Seems like an expensive toy for a little girl!  She also has access to a messenger bird -- probably not a cheap item either.  Yee-Li comes across as a little bit sharper and a little bit sneakier than the other club members in Ba Sing Se.

In The Promise, this character only has three lines of dialog, but she goes on to appear in The Rift and North and South Part One.  In one scene from The Promise, there is some dialog spoken by several members of Aang's fan club, and it's not clear which girl says what.  We will ask that our VA for Yee-Li (and other actors) read those lines as well, and we'll use the best takes in the final product.  Since Yee-Li is a character never seen in the TV series, there is no reference for this voice.  Bring Yee-Li to life!