In addition to directing, Whedon will also write and produce the untitled Batgirl standalone project, which will be his first film venture since Avengers: Age of Ultron. The report also adds that the idea for the film was conceived within the last month, so at this point in time, it's still uncertain whether the superheroine will ultimately make appearances in The Batman or Gotham City Sirens.
Whedon had previously expressed interest in directing a female-led superhero movie, specifically naming both Black Widow and a female-only Avengers movie as potential ideas that interested him in the past, but alas, neither project ever generated much traction with the higher-ups.