Cool tomboys

The name Jo still evokes the spunky image of the character in Louisa May Alcott's Little Women. Its literary status makes Jo one of the OG boyish nicknames for girls, ala Frankie, Billie, and Stevie. If you like that form, you can lengthen it to Joey.

The short but solid Irish surname Shea works well for both genders thanks to its soft, succinct sound. The traditional Irish form is Séaghdha, though it could also be used as a short form of Séamus, connected to James.