Paninya is, when first introduced, a petty thief from Rush Valley whose parents died in a train crash when she was a child. She lost both of her legs in the accident (and, in the first anime, also lost one arm). Dominic, a gruff, little-known mechanic at the time took her in as if she was his own daughter and took care of her. He gave her automail limbs to replace the ones she lost.
In the manga
Upon Edward, Alphonse, and Winry Rockbell's first arrival to the automail town of Rush Valley, Edward's silver pocket watch -- his sole identification as a State Alchemist -- is mysteriously stolen from him. They are immediately informed that it was most likely the work of the infamous local town thief, Paninya, and subsequently where to find her. In a small collector's shop not far off, Paninya is attempting to sell the stolen artifact when Ed finds her and confronts her about it. The two then engage in a wild chase throughout Rush Valley in which Paninya, utilizing her quick reflexes and tricks (one leg concealing a carbon blade while the other a 1.5-inch carbine), manages to stay one step ahead of the young alchemist. She is ultimately never caught by the Elrics, but by Winry instead, who forces her to return the watch and proceeds to befriend Paninya if only for her admiration of other's automail.
Paninya, under Winry's request, takes them out to the remote shop and home of Dominic, the man who gifted her the automail legs. Once there, they meet Dominic, his son Ridel, and pregnant daughter-in-law Satella. Paninya recounts her tragic beginnings, and how she was virtually saved by Dominic to Winry, who is prompted into asking the old automailer for an apprenticeship under him, only to be turned down multiple times. In admiration of Winry's resolve, Paninya vows to never steal again and instead use her talents to find an honest job in which to repay Dominic for everything he has done for her. When Satella unexpectedly goes into labor, it is mainly Paninya who aids Winry in delivering the baby, confessing her great disdain for the sight of blood to the others.
Paninya is again seen upon the Elrics' second trip to Rush Valley, having "turned over a new leaf" and working to help others around the town. When the Elric brothers are confronted by foreigners from Xing, Paninya rushes over to help Alphonse in stopping Fu, Prince Ling's retainer.
Her last appearance in the manga was in a photo from several years after the main story, where she was still friends with Garfiel. In the anime adaptation however, she is last seen in the Elric family photo, along with said family and Garfiel.
- Presumably, the reason why the first anime decided to give her an automail arm (she only had two legs in the manga) was so that Edward and company could meet her during the Automail arm wrestling competition.