The decision, apparently, was made by Bicondova herself, as she explained on social media in a letter meant both as an announcement and a farewell to fans of the Batman-adjacent series.
— camren (@camren) April 19, 2019
Apparently, the episode features a 10-year time skip, and Bicondova didn’t feel it was appropriate for her to play a decade-older version of the iconic cat burglar. Thus, the decision was made to recast Catwoman as Lili Simmons (Westworld, The Purge).
Bicondova emphasises in the letter that this was her decision, and that she’s very excited to see Simmons take up the reins of an older Kyle.
The final episode of Gotham airs this Friday, April 26, on FOX8.