Warning! Spoilers ahead for Supergirl’s season 6 premiere.
Supergirl season 6 just sent Kara Danvers to the Phantom Zone. The Arrowverse series began its final season with a major cliffhanger that saw Melissa Benoist’s titular character zapped to the Phantom Zone — a Kryptonian space prison that also functions as a parallel universe where time is effectively warped — by the diabolical Lex Luthor (Jon Cryer). The ending to the Supergirl season 6 premiere, called “Rebirth,” is shocking on many levels. But, while it works to intensify the story the show is telling, Kara’s send-off is included to accommodate Benoist’s real-life maternity leave following her pregnancy, which she announced in March 2020.
Supergirl and friends may have stopped Lex from brainwashing Obsidian VR users into loving him and eradicating the other half of the world. However, the scheming villain had another plan up his sleeve before all was said and done. During the final showdown in the Fortress of Solitude, Lex is outnumbered, but he has just enough time to grab the Phantom Zone projector and zap Supergirl there right before Alex takes him down. The season 6 premiere ends with Supergirl inside the Phantom Zone, unable to be reached by the rest of her team because the projector’s data has been wiped and is potentially unrecoverable (at least for the time being). When Lena offers to find Kara by way of a transmap portal, similar to the one she used during the “Crisis on Infinite Earths” crossover, Brainy says it won’t work because they don’t know exactly where Lex sent Supergirl within the Phantom Zone.
Sending Kara to the Phantom Zone works to accommodate Benoist’s maternity leave, which delayed her return to Supergirl by a few months. The actress announced the arrival of her first child with husband Chris Wood (who played Mon-El in previous seasons of Supergirl) in September 2020. Filming on Supergirl season 6 began in October 2020, though Benoist herself didn’t return to filming until January 2021. While Kara is seen inside the Phantom Zone at the end of the season 6 premiere, unconscious and surrounded by other aliens, her disappearance effectively removes Benoist from the main plot of the show for a while.
What’s more, keeping the actress siloed from the rest of the cast likely made it easier to film her scenes for Supergirl when she returned in the new year, all while the remaining actors could continue filming in the months Benoist was on leave. Kara’s absence heightens the tension on the show, at least until it’s time to rescue Kara from the Kryptonian prison. It’s unclear how often Supergirl will show Kara from within the Phantom Zone and how her story might connect back to whatever’s going on in National City during her absence. However, sending the superhero to the grim location presents a realistic excuse for her disappearance, with her friends already working overtime to provide viable reasons for Kara’s absence from CatCo (this time it's that she's with Cat Grant investigating a story).
Throwing in an additional obstacle that prevents the Supergirl team from bringing her back to Earth so quickly ensures that Benoist gets a break for her maternity leave and likely eases the transition surrounding the actress’ delayed return to filming. What's more, being separated from the primary cast means Benoist won’t have to be edited back into any of the scenes they’ve already filmed. Exactly how many episodes it will take for Kara to be saved is unknown. This may also mean her character might have limited screen time in the beginning of Supergirl season 6, which is a sad thought considering it’s the final season. Either way, the workaround is clever considering the circumstances.