So we were speculating that the new Batwoman in Batman Beyond would be revealed likely by issue #40.
We got a hold of some Batman Beyond #41 solicitations that clue in that her identity is known by this issue, by either revealing her identity in issue #40 and or definitely in issue #41.
See the below spoiler images of the solicitations for Batman Beyond #41.
And now zoomed in on the text.
This new Batwoman made her debut in Batman Beyond #37. Once we know the true identity of who's behind the mask and suit, we'll all find out if this is a new character or existing (which all signs point towards since the solicitations make it seem like it's going to be an existing character in the Beyond Universe).