As mentioned above, Krypton and The Royals actress Wallis Day has indeed taken on the role of Gotham’s former protector, the original Batwoman Kate Kane. In the episode itself, Kane appears heavily burned and bandaged in Gotham City’s sewers, leaving her unrecognizable as the Ruby Rose version of the character. As such, Day herself did not actually make an appearance in the episode.
As revealed by the most recent episode of Batwoman (via TVLine), Kate Kane, previously thought to be deceased by the show’s characters and fans alike, is in fact alive. However, it’s not Rose who is playing the character anymore, as Krypton’s Wallis Day is taking on the role