Milly Alcock has been preparing to play Supergirl, receiving advice from others, including an unnamed piece of advice that mentioned "battle scars" and guidance from David Corenswet. Alcock has also spoken about her approach to the role, noting that past Supergirl stars are "just people" and not a source of advice for her. The production of Supergirl has involved physical challenges, with Alcock reportedly accidentally punching a stunt double during filming, and also explores a sister dynamic, possibly with Eve Ridley.