Penelope Victoria “Penny” Sanchez is a male-to-female transsexual with brown hair and glasses. He's one of Rudy's classmates, and an overachiever, with a fascination for science. Other than Rudy, He's the only human who knows about Chalkzone because he travels there often with Rudy. The song "Escucha Mi Corazon" taps into his Latin roots, since he can be heard singing the song in Spanish. It is also speculated that Rudy and Penny have a love interest for each other. He 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.