Between its lengthy runs as an animated series and numerous comic books, Batman Beyond has become one of the most popular versions of Gotham's future, where Terry McGinnis carries on Bruce Wayne's war on crime. Like Wayne himself, several hallmarks of Bruce Wayne's Dark Knight have lived on or been echoed within this world, including some of Gotham's other famous residents. The original animated series revealed the tragic end of Mr. Freeze and the strange fate of the immortal Ra's al Ghul, but not every major character made it onto the screen. Though Dick Grayson was mentioned, he didn't meet Terry McGinnis until Batman Beyond continued in the comics.
And even though a new character rose up to take her place, the final fate of Selina Kyle, Catwoman, was left even more uncertain.
Selina is one of Batman's greatest loves so, of course, this romance made its way to the DC Animated Universe. Though there was a lot of flirtation in Batman: The Animated Series, it never moved beyond that, not getting close to anything like the relationship the two have in comics now. By the time of Batman Beyond, Selina Kyle was just another in a long list of lost loves for the retired Batman.
Her picture was along with the likes of Zatanna, Lois Lane and Barbara Gordon in the episode "Out of the Past" which saw the return of old flame Talia al Ghul. A mannequin of her can be seen in "Black Out" alongside those of many other Gotham rogues. Finally, Bruce mentioned her by name once, as he gives Terry advice on dealing with his own criminal love interest - Ten of the Royal Flush Gang.
Besides these cameos and references, Selina Kyle's fate in the Beyond universe has yet to be revealed. However, that doesn't mean that the legacy of Catwoman hasn't continued into Neo-Gotham. Terry McGinnis encountered his very own feline thief in Batman Beyond: Hush Beyond by Adam Beechen, Ryan Benjamin, John Stanisci, David Baron and Travis Lanham.
In this story, the new Catwoman had no connection to Selina Kyle, Batman or any other famous Gotham face. Though Terry had his hands full fighting a new version of Hush, he did eventually learn the true identity of this version of the cat burglar. She was the secret daughter of the Firestorm villain Multiplex and shared her father's ability to create duplicates of herself. The reason why she chose the name Catwoman despite having zero connection to the original is that, unlike her father who had no limits to his powers, she can only make up to nine copies of herself - giving her literally nine lives.
Like the original Catwoman, she was highly skilled in acrobatics and was able to evade the new Batman. Another thing she shared with Selina Kyle was her moral ambiguity. Though she was happy enough to steal, she also helped Terry and Dick defeat the new Hush. But unlike Selina, the new Catwoman had no romantic interest in her Batman.
Batman Beyond's Catwoman hasn't returned in the comics since her first appearance, however, that doesn't mean she can't still turn up again in the future. Unfortunately, her existence still doesn't shed any light on Selina Kyle's Neo-Gotham fate. However, the Batman Beyond 20th Anniversary panel at SDCC 2019 had series co-creator Bruce Timm reveal scrapped plans for a direct-to-video movie that would have revealed what happened to Selina in the DCAU's future.
In the movie, Selina would have been a wealthy businesswoman and the main villain in the story. It would also have been revealed that she had cloned Bruce Wayne to create Terry McGinnis, essentially making her Terry's mother. Of course, this idea was reworked into the Justice League Unlimited episode "Epilogue" where Amanda Waller was revealed to be the one responsible for Terry's creation, also using Bruce's DNA.
The fact that the scrapped plans for Selina no longer fit with Batman Beyond's established lore means that her fate in this future is still a mystery.