The "Avox Girl", as Katniss Everdeen called her, later turns out to be named Lavinia.
Katniss calls her the "Avox Girl" because she is an Avox, or a traitor enslaved by the Capitol. Since her tongue has been cut out, she cannot speak.
Katniss first meets Lavinia in the woods outside District 12. She witnesses her with a younger boy, escaping from something. Lavinia and the boy are running through the trees when a hovercraft appears out of thin air and captures them. Just before their capture, Lavinia, described as having red hair, looks up at Katniss and silently asks for help.
Because of this, Katniss has always felt guilty and somewhat responsible because she never did anything to stop what happened.
When Katniss runs into Lavinia again as a maid servant for the Capitol, she immediately recognizes her and almost says something, but then stops herself for fear of getting the girl in trouble. Effie Trinket notices that Katniss recognized her and exclaims that it is impossible that Katniss would know a traitor, so Peeta Mellark quickly covers up with an excuse, stating that the girl resembled another classmate at their District 12 school - Delly Cartwright.
In the end, Lavinia holds no grudge against Katniss and instead wishes to please her as best as possible.