Editor's Note: The following contains The Flash spoilers.The Flash takes on an epic story of time travel, alternate universes, and personal traumas, making it one of DC's more ambitious films. Along the way, it introduces Supergirl (Sasha Calle) into the DC Extended Universe but squanders the opportunity by not making her everything she could be. It's not as if they ruined the character entirely, but they didn't give her the introduction to the universe she deserved. Since Supergirl isn't as popular as many of DC's heroes, she could be relatively unknown to the general audience, and The Flash doesn't do much to change that.
The problem lies in the story Supergirl got in The Flash, not the actress. Calle's portrayal is good for what she had to work with. But the fact is, Supergirl isn't as large a part as fans were led to believe. With the film's time travel shenanigans, and this is the only time the character will appear as this particular version, it left something to be desired. The film depicted her as a female version of Superman, borrowing his plot and ignoring the things that make them different. While it's exciting to see a new hero on screen rather than a reboot of a familiar character, this wasn't the perfect introduction for Supergirl.
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While it may seem obvious that Supergirl isn't the main character, she's not in very much of the film, aside from the climactic battle. With many heroes appearing in The Flash, some get more time than others, but in Supergirl's case, the advertising was misleading. From all the trailers, she seemed to be a relatively significant part, whereas, in the film, she had a few stellar action sequences and a brief appearance. She's not introduced until well into the story after Barry Allen (Ezra Miller) is trapped in the past, which he changed, and discovers that it is very different from his universe. Barry gets his former self powers and finds Batman (Michael Keaton) before they go to find Supergirl.
Once she is saved, Supergirl shows off her incredible powers but quickly leaves again, not caring if humans are destroyed as they were never kind to her. Obviously, her imprisonment resulted in trauma, not to mention the destruction of her world and her entire family dying. Yet none of that is addressed, and she has a rapid change of heart, making her ready to become a hero for the people of Earth. She flies Barry into a storm to get his powers back before they face Zod (Michael Shannon). Her fight against the Kryptonian villain is her most impressive scene, but ultimately, it is doomed to fail, and Kara Zor-El dies along with Batman. Supergirl gets very little focus as the emotional beats follow Barry. This is understandable as he is the lead, but it is still a letdown as The Flash marks Supergirl's first film appearance in nearly 40 years. While she may be important to the final battle, the character receives little development and is just not that big a part, which undermines her introduction.
The lack of focus on Supergirl could be excused if her brief appearance set up bigger things for the character, but that isn't the case. As the franchise is preparing for a reboot, this is her only chance to appear in this iteration. With James Gunn and Peter Safran taking control, DC is getting a new set of movies called the DCU. This franchise will feature Supergirl, but not this version, as The Flash deals with an alternate where Zod wins. It's unknown if Calle will return, but whoever plays her will be a different Kara, making the character in The Flash a one-off who was significantly underused.
Supergirl's part in the story is small for it to be her only appearance. The Flash allows for the reappearance of Keaton's Batman, giving an end to a long-standing character, but this Supergirl has no history outside of the movie. While the character's appearance is notable in itself, as Supergirl isn't in many films, she is a glorified cameo who isn't from other content. With no hope of expanding the character, the inclusion of Supergirl left something to be desired.
Perhaps the worst part of The Flash's Supergirl introduction is that she's not really Supergirl. The film deals with an alternate timeline where Kal-El was killed before becoming Superman. Barry's search for the alternate version of his friend leads him to Kara. The plot essentially replaces Man of Steel's Superman with Supergirl rather than giving the character a more traditional Supergirl story. And it doesn't even stop there. Not only is Supergirl placed in an alternate version of the Man of Steel fight, but her entire story is adapted from a few of Superman's, specifically Superman: Red Son, where Superman's pod lands in Russia, and Flashpoint, which shows him locked away in a government facility.
The Flash makes Supergirl into a rip-off of her cousin, where their comic versions are distinctly different. Part of what separates them is that Supergirl remembers Krypton, whereas her cousin doesn't. The film never addresses this. While Supergirl was seemingly still older than her cousin, as she was sent to Earth to care for him, she appears to have little memory of it. Superman has been seen in several movies since Supergirl's last appearance, making this the perfect opportunity to highlight their differences. But, despite the wide familiarity with Superman's story, The Flash does little to differentiate the two Kryptonian heroes. Supergirl isn't nearly as recognizable as her cousin, and introducing her as essentially a girl version of Superman does a disservice to the character and her history. This dark version is interesting, but with a hero not as commonly known as most, it's also a strange introduction to the character. The Flash fumbles what could have been a pivotal debut of Supergirl to a broader audience.