Squirrel Girl (real name Doreen Green) is a superhero with the ability to control squirrels. She also has squirrel powers, and a squirrel's tail.
Squrriel Girl's name can be seen on one of the news tickers promoting her new line of perfume.
Her name and picture also appear in the episode Sandman Returns. As Spiderman checks if he's still the number one superhero in New York, he's shocked to find himself listed on place 15 in the poll. Behind Hawkeye, Nova and Squirrel Girl. While he knows Hawkeye and Nova, he wonders who Squirrel Girl is.
In the episode "The Next Iron Spider", she appears at the beginning defeating Juggernaut with her squirrel army, though he actually feigns this defeat. Her squirrels Tippy-Toe and Monkey Joe also appear.
In the episode "S.H.I.E.L.D. Academy", she's seen as a student at the Triskelion's S.H.I.E.L.D. Academy.
In the episode "Burrito Run", Squirrel Girl sneaks out after hours for late-night burritos with Spider-Man and Power Man and along the way they must contend with some of Spider-Man's enemies.
In the episode "Nightmare on Christmas", she appears in a S.H.I.E.L.D. base hibernating with her squirrels when Spider-Man comes in and asks her where his teammates are.