Pia is Abraham Bowman's girlfriend, they are about the same age. Because of her activities with her cousin Pedro, and later with her boyfriend Bram, looting supplies from the other side of The Wall, Pia has access to goods not normally available under The Occupation, such as the expensive headphones she gives Bram in "Brave New World".
Before The Arrival Edit
We don't know anything specific about Pia's life before The Arrival.
After The Arrival Edit
In the episode "98 Seconds" Pia asks for Bram's help with her cousin Pedro who has fallen and hurt himself in a tunnel that leads under The Wall. Pia knows about the tunnel because of her father's job before The Arrival (he used to work for the water and power company). It turns out that Pia and Pedro have been going on supply runs to the area on the other side of The Wall which is deserted but still has stocks of food etc. Later on (in the episode "Blind Spot") Pia takes Bram on one of these supply runs.