Penelope Victoria “Penny” Sanchez is a young girl with brown hair and glasses. She's one of Rudy's classmates, and an overachiever, with a fascination for science. Other than Rudy, she's the only human who knows about Chalkzone because she travels there often with Rudy. The song "Escucha Mi Corazon" taps into her Latin roots, since she can be heard singing the song in Spanish. It is also speculated that Rudy and Penny have crushes on each other. She has a Boston accent, very similar to Barbara Walters.
From season 1-3 Penny wore an olive green sweater, a green plaid skirt, ankle socks of the same olive color, and red-brown sneakers. In season 4 Penny's appearance changed. Penny kept the same skirt, but now wore an olive green tank top and sandals similar to her old sneakers.
Penny first appeared, but without any real introduction, in the Oh Yeah! Cartoons short "Rudy's Date". In the short, Reggie Bullnerd erased the scientific formula for perpetual motion that she had written on a chalkboard. Willing to help, Rudy brought her with him into the ChalkZone to retrieve the formula. Snap reluctantly helped them find the pieces of the formula, most of which had been stolen by Butch Biceps (he had used the variables to decorate his motorcycle jacket). Penny since then became a regular on ChalkZone well into when it became its own series, where her introduction was revised, in the episode "Rudy's Story". In that episode, Penny was introduced as Plainsville Elementary's new student, whom Rudy is obviously attracted to. Rudy explained his "vacation" in ChalkZone to her, but although she found the story interesting, she assumedly didn't find it "scientifically possible" until the events of "Rudy's Date", which occurred later.
In addition to solving mathematical and scientific problems, Penny is also willing to help Rudy and Snap (whom she seemingly finds annoying, and vice-versa) when needed. Penny's friendship with Rudy nearly fell out once, in the episode "Power Play", when he faked his science project by drawing a machine that produced Bobbleheads of Snap, which led the egocentric Dr. Von Dockter to believe that Rudy had discovered the secret of perpetual energy. Penny was at first furious that Rudy had used the dimension he was defending to cheat on a science fair, to the point that she practically broke his heart. But after Dockter and his men dragged Rudy and his parents away for scientific research, Penny set her anger aside and used the Magic Chalk herself for the first time in order to help Rudy out of his predicament.
Another time Penny proved her heroism was the episode "Chalk Queen", where she had another argument with Rudy, as he had forgotten to provide illustrations for her biology report. She was then captured by Skrawl, who tried to get her to help him take over ChalkZone. She pretended to agree, and then, once Rudy had dueled with her for a bit, Penny revealed that her going along with Skrawl's plan was all just an act, and she eventually forgave Rudy again.
It's very obvious that Rudy has a large crush on Penny, as he has the tendency to stare lovingly at her whenever she talks scientifically.
She was voiced by Hynden Walch, who also happens to be the voice of Princess Bubblegum in Adventure Time and Summer Hugglemonster in the Disney series Henry Hugglemonster and Debbie the Bride from the 1993 comedy film, Groundhog Day.