As Superman's cousin, Supergirl has had a lot to prove in the past to overcome the position she was pushed into as Kal-El's "sidekick." But after years of fighting, her own adventures finally took root, and she was able to push past the ridicule and doubt. She even eventually proved she was stronger and more resilient than Superman had ever been shown to be before.
Supergirl: Woman of Tomorrow was a limited series that ran from 2021 to 2022 and pushed the limits of what Kara Zor-El is capable of, establishing her as one of the best heroes in the known universe. It shows a side of her so rarely seen in DC and allows her to grow into her own. Her determination and resilience have a spotlight shown on them throughout the series, and in one fell swoop she shows strength that outmatches even Superman's.
In a display of might, Supergirl proves she can outlast Superman under the influence of Kryptonite in Supergirl: Woman of Tomorrow #5 by Tom King, Mat Lopes, and Bilquis Evely. Having been trapped on a world built to hold Superman with a green sun made of Kryptonite, Kara is forced to wait out until the setting of the sun. Quickly, she reveals that Kal-El himself only survived under the sun for 45 minutes before being rescued by his fellow Justice Leaguers, but he described the experience as the "closest to death he ever got." With that in mind, it seems impossible that she will last ten hours on this world without succumbing to the Kryptonite's influence. However, not only does she survive, she also continues to fight and recovers almost as soon as the sun has sunk below the horizon.
Supergirl Can Withstand Kryptonite Better Than Superman Can
Fueled by pure adrenaline and determination, Supergirl's run-ins with Kryptonite have shown her strength many times over, as she has been able to push past the effects and fight on. Another one of her powers however, is that she is immune to synthetic Kryptonite, whereas Kal-El is not. During a run-in with Poison Ivy in Supergirl #0 by Jeff Loeb, Ian Churchill, Norm Rapmund, Christina Strain, and Richard Starkings, she is unaffected by the synthetic Kryptonite that Ivy is using. On the other hand, Superman is weak to the effects of it and succumbs to Ivy's control, while Kara is easily able to fight off Ivy. With this advantage, Supergirl has shown that she can face threats that even Kal-El cannot face, such as Lex Luthor and his affinity towards creating synthetic Kryptonite to battle the Kryptonians.
Her first run-in with Kryptonite was in Action Comics #262 by Robert Bernstein, Wayne Boring, Stan Kaye, and Joe Letterese. Supergirl discovers a Kryptonite meteor in a forest, and tries to build an immunity to the rock by pushing herself to get closer and closer every day. By working towards building up resilience against the rock, she displays incredible mental fortitude and a stubborn determination that even Superman acknowledges is rather impressive. Her curiosity and drive to overcome the Kryptonians' weakness makes her more resilient than Superman, as she is not content to just accept that she will forever be susceptible to Kryptonite's power.
While many underestimate her and consider Kara to be a softer hero than Superman, her nature shows pure, unbridled determination and stubbornness — feats she overtakes her cousin in. With her persistence, she's able to push past any limits placed that hinder Kal-El, even going so far as to beat their own natural enemy. Kryptonite may be deadly to them, but Supergirl has long since proved that her strength outlasts Superman's in this battle against the element.