Meng lives in a village below Mt. Mahaku in the northern region of the Earth Kingdom, and is the young assistant for Aunt Wu.
Part of her job includes greeting Aunt Wu's guests and bringing them snacks.
Meng is a bit younger (and shorter) than Aang, and also had a major crush on him from the moment they first met. Part of this crush may have been influenced by Aunt Wu, who prophesied that Meng was destined to marry a man with big ears. The fact that "meng" and "aang" sound similar also seemed important. Throughout the day Meng stalked Aang and dropped giant hints of her crush on him, but he stayed oblivious. Or worse, used her ideas to try impress Katara.
As hard as she tried though, she eventually gave up when she realized where Aang's heart lay. Despite her disappointment, she helped him by giving him Aunt Wu's cloud-reading book. With it, Aang could convince the villages that Mt. Mahaku was about to errupt, and in doing so would destroy the village.
Nothing else is mentioned about Meng's past, or her family, if she has one. Although it is certainly clear she thinks poorly of Katara, even going so far as to call her a "floozy". ^^;