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 a love interest for each other. She has a Boston accent, vary 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.
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.