Note that this is Batwoman (Kate Kane), not Batgirl (Barbara Gordon). She’s still based in Gotham City, though.
The character will be introduced during the annual crossover. According to other news, Legends of Tomorrow will not be included in the crossover. My guess is that the crossover will take place on Earth-38, where Supergirl lives. It seems like a natural fit to have Batwoman and Supergirl interact more.
Supergirl is a lesbian too? :dubious: 
Her sister is.
Very au courant.
Please don’t be all angsty. “Kate must overcome her own demons sounds” like it will be angsty.
Is Batwoman at all light-hearted or dark comedy or is she a serious hero like the Green Arrow?
In fact, in the comics Batwoman dated Maggie Sawyer–who was Alex Danvers’s girlfriend on Supergirl.
Meta.
I hope they make it like Gotham and go super-outré. Especially since Gotham will be ending next season and there isn’t anything else in that niche. Bring on the weird and wacky while still somehow retaining the grittiness.
I wouldn’t be surprised if Renee Montoya showed up. According to the wikis, she eventually became the Question. Hmmm…
The comic is very angsty.
Here’s a trailer from the CW that teases the arrival of Batwoman: - YouTube
It’s just clips from past episodes, but the way it’s structured implies that Batwoman will indeed be a part of Supergirl’s Earth-38 rather than Earth-1. Of course, it also includes Black Lightning which is explicitly not a part of the Arrowverse (for now), so who the frak knows?
I’m kind of irritated by Supergirl apparently not know the identity of a masked person, Given the wide array of super-senses a Kryptonian supposedly has, she might not even notice the person she’s addressing is masked, having already identified the person by smell, heartbeat, the particular arrangement of blood vessels as visible in infrared and skeletal structure as visible via x-ray… We mere humans might recognize people by sight, but I’d expect Supergirl to casually collect vastly more information about a person, to where masks and disguises are trivial, even laughable.
Not that she would laugh, as that would be rude.
The masks are of course lead lined. 
That’s how they explained Supergirl not knowing who Guardian was underneath the mask. Of course, Cat Grant could immediately identify that he was Jimmy Olsen because he left his eyes unconcealed.
Ruby Rose has been cast to play Batwoman. I’m unfamiliar with her work, so I can’t say whether this is a good fit.
I’m meh on Rose - she plays pretty much the same character in everything I’ve seen her in. I think the casting is a mistake because they’re using the appearance as a sort of back-door pilot for (yet another) CW superhero show and I seriously can’t see the actress dropping her movie career to star on a series. That means that if they wind up doing a series they’ll have to re-cast the lead.
Although the Batwoman series is still in development, it is being reported everywhere that Ruby Rose would be the lead. So, not re-cast; it’s just still in development.
According to IMDB, she’s had some supporting roles in a few movies. Doesn’t seem like much of a movie career. She probably would prefer being the lead in a TV show, which also comes with a steady paycheck.
It’s on the CW. Even without knowing the comic, I can tell you it’s going to be angsty.
What I’ve seen on Reddit is largely people claiming she’s not a good actor. And this was from people who were optimistic about the show saying that they now were no longer. And it wasn’t because she is LGB, as they recommended others who they thought would be better.
I do think she at least looks the part. She has that type of face that looks good below the cowl. (When I look at superhero casting, I always consider looks.) But I myself have not seen her act in anything, so I do not know.
Her stint on Orange is the New Black tended to be how most people knew of her. I never got into that show.
Based on this USA article, the people on Twitter saying she’s a good idea are all fellow actresses, while those who think she is bad actress or a problematic LGBT actress are all regular people. Interestingly, all the comments are from women.
Screw being on the CW, it’s Batwoman…Kate’s life is full of angst. From the alcoholic haze she spent much of her time in after getting DADT’d out of West Point, to her engagement ending because her fiancee (Maggie Sawyer, as a sidenote)'s ex threatened to sue for custody of their child, to the fact that her main villains have included her (brainwashed) twin sister, and one of her (not-brainwashed) lovers.
Ruby Rose is 130 pounds. There is no way someone that small is going to be an effective street fighter. Wonder Woman, Supergirl, and Buffy all have powers that make them superhumanly strong. The appeal of Batman/Woman is that they are regular people who are highly skilled. She is going to need to seriously bulk up for the role.