Squirrel Girl was the sidekick of Dark Owl.
History
In order to evade NSA Agents West and Rush, Zeta and Ro fled into a Picto-convention. They holomorphed into Dark Owl and Squirrel Girl, but the disguise quickly fell through.
Bucky later commented that Ro looked good as Squirrel Girl.
Background information
Squirrel Girl is based on the concept of Robin and Sparrow. To date, the only character named Squirrel Girl was a plucky comic relief hero from Marvel named Doreen Green.