Bai Xiaochun met her in Ovens and She's a Girl. She was one of the "Fatties", and Bai Xiaochun knew her as the Third Fatty and thought of her as elder brother. It is only when the three of them join the outer sect that her gender is revealed to him by Big Fatty Zhang.
She gets sent to the Green Crest Peak as an outer sect disciple
Later, when the chicken-stealing fiend haunts the sect, Bai Xiaochun and Big Fatty Zhang also enlist her into their group of thieves, but eventually have to give up on stealing chickens.
After the chosen battles (ch. 98), it is revealed that she has some talent of her own:
“Now that you mention it, his friend, that girl who also came from the Ovens, Qingrou, is actually quite impressive. She might not measure up to Tianyou, but she has her own special destiny. She seems connected to Green Crest Peak’s mountain defense sword. She’s currently seeking enlightenment in Green Crest Cave, and if things go well, Green Crest Peak will soon have another spirit sword guardian!”
Much later, when Bai Xiaochun returns from the Blood Stream sect, she appears again.
"Third Fatty Hei was actually a slender young woman. Her skin wasn't very fair, but she was tall and heroic-looking."
She was in the third wave that went to war, and participated in a big party in the Ovens the night before.