WARNING: The following contains major spoilers for Batwoman Season 1, Episode 8, "A Mad Tea-Party," which premiered Sunday on The CW.
Ever since Kate Kane discovered Alice is actually her sister Beth, believed dead for fifteen years, in the show's pilot, Batwoman has put an emphasis on sisters. However, during this time, Kate has ignored her step-sister, Mary, who wonders why she’s not good enough to get the same attention as Alice. This came to a head in the mid-season finale, when Alice murdered Catherine Hamilton-Kane, Mary’s mother and Kate’s step-mother. This sets up a new direction for Kate, as Beth is gone and Alice isn’t worth saving.
But what does it mean for Mary? She’s just lost her mother because Kate refused to do anything about Alice. She’s also in the dark about her sister being Batwoman, putting her at odds with the title hero. The show seems unlikely to give Kate another evil sister, but these recent events could instead push her to take on the identity of a hero herself.
Mary already meets a lot of the requirements for a hero. She has a public identity (big social media influencer) and is hiding a secret life (running an illegal clinic for those who can’t afford hospitals), all while getting through medical school. She’s already doing many great things, which her mother reminded her of shortly before her death, so she's already a hero, not "becoming" one.
This is a show based on DC Comics, though, so almost everyone gets a costume or secret identity at some point. Even a code name would do, as Arrow did with Felicity becoming “Overwatch” and Diggle being “Spartan.” Although there's no prominent character in the comics that Mary is apparently based on, there are some she could potentially be, though many would be in name only.
Nightmare Nurse
This would be a pretty much in name-only adaptation, but the name at least fits quite well. Mary works at night in Gotham, a nightmare of a city. Mary has also dealt with and saved horrible people, some of them with terrible injuries, which she told Kate in the mid-season finale, talking about gang member she’s helped without getting any thanks or credit. Sure, Mary doesn’t have the demonic or magic background to make this a more faithful adaptation of the character, but it’s a great name to use and -- who knows -- there’s always the possibility for future plot and character developments.
Doctor Mid-Nite
Mary isn't a doctor yet, but when has that gotten in the way of a good superhero name? In the case of all the different versions of Doctor Mid-Nite (sometimes spelled Doctor Midnight), they’ve all been doctors when taking the name, and Mary could be by the time she starts using the moniker. Her taking on this name might also be a bit of foreshadowing: one of the defining aspects of every iteration of Doctor Mid-Nite has been their blindness. This would also play into the character’s legacy side in the comics: there have been three different versions of Doctor Mid-Nite, and we’ve already seen a Doctor Mid-Nite in this universe, having appeared as part of the Justice Society of America in the second season of Legends of Tomorrow. As that was in the past, there could still be room for a Doctor Mid-Nite later on in the timeline.
Ri
Don’t worry if you don’t recognize the name. Ri was a minor supporting character in Batman Confidential and Justice Society of America shortly before the New 52 wiped the continuity. Rather than taking on the name, however, Ri would likely be the basis for superpowers, if they become more of a presence in the show. Ri has the power to heal others, a perfect fit for Mary and what she's already doing for the people of Gotham. Plus, Ri was actually created by Marc Guggenheim, who has been one of the main architects of the Arrowverse.
A New Name or Identity
From the introduction of her secret life in the pilot, Mary Hamilton has stuck out to fans as being a compelling hero already. Following the death of her mother, she’s going to have a lot to process. With Kate Kane already having one villainous sister in Alice, they’re probably not going to go the villain route again. Instead, this may push her to become more of a hero than she’s been already, complete with a code name to go with her current secret identity. With the Wonderland Gang causing chaos in Gotham and Kate finally deciding that Alice isn’t worth saving, Batwoman will need all the help she can get (once she's done with the Crisis, that is). This help might even just give the two step-sisters the chance they need to grow closer.