Ying left her hometown with her husband and sister-in-law to travel to Ba Sing Se, where they planned to start a safer life for their child. When things became grave, Ying held on to hope that she and her husband would make it and, with a little help from AvatarAang and Team Avatar, they did. She was nine months pregnant when they met Team Avatar.
Ying and her family were spotted by Zuko while the banished prince was traveling alone. He almost decided to steal from her husband, but changed his mind when he saw that Ying was pregnant.
Aang and his friends had just decided to traverse the Serpent's Pass to get to Ba Sing Se when they were approached by Ying and her family. Katara invited them to travel with them, but the family told them that the Serpent's Pass was far too dangerous. Instead, they planned on traveling via an underground ferry system at Full Moon Bay that carried refugees to the city. Aang and the others agreed to travel with them.
At the ferry terminal, the clerk turned out to be extremely strict and ruthless. Ying and the family sought Aang's help upon discovering someone had stolen all their belongings, including their passports and tickets. Aang tried to persuade the clerk to give them replacements, but she refused, complaining that she could not bend the rules. With no other choice for the family, Aang gave up their tickets and offered to guide them through the Serpent's Pass.
The group reached the pass, which, seemingly against its name, was very straight and narrow. Much of it was barely wide enough for people to pass through single file. Ying seemed to lose hope, and Aang said that perhaps it was best that they did abandon their hope and instead focused on the present need to cross the pass.
After spending the night in the pass, the next morning Aang's group came to a large setback: a portion of the pass was underwater. Katara stepped forward, parting the waters to allow them to pass. As the path got deeper, Aang helped her, forming a bubble of air for them to walk underwater safely. As it turned out, the Serpent's Pass was named and feared not for its shape, but for the gigantic sea serpent that swam in the surrounding waters. The serpent attacked the bubble, forcing Toph to raise the sea-floor under their feet. This stranded them in the middle of the water, with the serpent circling around them. Aang attacked the serpent, telling Katara to get the others across while he distracted it. Katara created an ice bridge for the others to cross.
The group finally crossed the Serpent's Pass, just in time for Ying to go into labor. Katara, who had experience in midwifery, quickly took charge. The baby, a girl, was born with no complications, thanks to Katara. Aang, seeing the family coming together, renewed his hope, which inspired the baby's name: Hope.
Ying reached Ba Sing Se with her family and was living in the Lower Ring. They entered the city on the same monorail car as Zuko and Iroh. Iroh commented on how beautiful her newborn baby was.