Batwoman is one of the curious cases in the Batfamily, as she technically wasn't choosen to be in the family, but rather was added on cause it was clear she wasn't going away.
Katherine Kane has taken on several forms in the comics, including being two separate women by the same name. But in both cases she's a wealthy heiress who gets inspired by Batman and decides to suit up. In her modern day reboot, she came when Batman disappeared during Infinite Crisis.
Not only is she an outsider of sorts, she's also gay, which made big news in the world when it was announced. And very different from the Silver Age version who was very attracted to Batman. Batwoman has stuck around for a long time, and was even the focus of the recent animated movie Batman: Bad Blood.