Role in the show
Penelope first appears (although is referred to by her real name), in the episode Legend of Candyface. But in that episode she was just a supporting character. She despised Sonny because she and Chad Dylan Cooper were in love, when she had a crush on Chad. Penelope then planned on pretending to be Sonny's friend before ruining her reputation and then killing her.
In Sonny With a Secret, Penelope frames Sonny for stealing a necklace from a mall and stealing her friend Grady's gold coin, ruining her friendship with So Random. She also exposes Chad's secret that he makes all his decisions based on fortune cookies to the paparazzi and frames Sonny for it, causing Chad to break up with her. Penelope also makes up a character named Vicky Sikowitz and passes her off as a real character to accuse Sonny of stealing her character "Sicky Vicky". As a result, Sonny's friendships are ruined and she is fired by Condor Studios.
Meanwhile, Sonny's best friend Tawni still believe Sonny and takes her out of L.A incognito so Sonny fire a cheese ball at her old high school's football game, as Sonny was scheduled to do. Later everyone deduces Sonny was framed and learn that someone has made a bomb into a cheese ball and realize someone is out to kill Sonny. Chad and the So Random Crew set out to rescue and apologizes to her and take off in Chad's private jet.
Mid flight, the jet's captain is revealed to be Peneople incognito, who reveals to everyone that she was the one who framed Sonny and planned on killing her, admitting her motive was all because Sonny loved Chad. Penelope intended to leave the So Random crew to die in a plane crash, but offered to let Chad live if he agreed to date her. Naturally (and sanely) Chad refuses. Penelope jumps out of the Jet with all the extra parachutes, leaving them to crash. Luckily Grady had a parachute on him, because his mother advised him to never get on a plane without one. They all jump together on the same parachute, although it rips on the way down due to their weight. By luck, they land next to Tawni's car.
At Sonny's old high school, Peneolope appeared as Vicky Sikowitz at the football game to take Sonny's place. Sonny and the others arrive just in time, and they tell everyone Sonny was framed. "Vicky" lies and says she only wanted attention and lets Sonny take her place, so that she'll get killed by the bomb. Because they haven't told her about the bomb, as Sonny lights the fuse, Chad pushes her out of the way, Zora stops the fuse, and Nico takes the bomb out before it blows. Penelope tries to make a break for it but is stopped and exposed by Tawni. After being exposed, Penelope is arrested.
She never appears again in the show, but likely got life in prison because she did attempt to kill five people.
- Even though her real name is Marta Balatico, she is nicknamed and referred to as Penelope because of the character she plays in the in-universe TV show MacKenzie Falls.
- Because of her attempts to kill Sonny and leaving Chad and the So Random crew to die, she is one of the darkest villains on a Disney Channel show (others being Gorog, Kaita, Jesse, Vice Principal Stern and Victor Krane)