According to Batman-News, Kiersey Clemons is not a part of the current cut of Justice League.
As I previously speculated, with WB having screened the Justice League movie, details are beginning to come out.
Regarding why Kiersey Clemons was cut from Justice League, if I had to guess, it was because she was being included to help set up the Rick Famuyiwa The Flash movie, and since Famuyiwa has since departed, Kiersey Clemons is no longer needed to appear. Rick Famuyiwa cast Kiersey Clemons as Iris West as the two worked together in Dope. Now WB is developing the Flashpoint movie.
That's also my guess why Jesse Eisenberg and Lex Luthor were cut from Justice League--because the Ben Affleck Batman movie is no longer happening. It's speculated Lex was involved with Joe Manganiello's Deathstroke in Justice League, but since Matt Reeves has thrown out The Batman script and is starting over, Deathstroke and Lex are not longer needed in Justice League, which may also mean Deathstoke has been cut from The Batman.
Of course it's entirely possible that both Lex Luthor and Iris West were minor roles, and that Joss Whedon made the decision to remove them because he felt they didn't fit with the movie.
Justice League has a November 17, 2017 release directed by Zack Snyder, with the story by Chris Terrio and Zack Snyder, the screenplay by Chris Terrio and Joss Whedon, and stars Ben Affleck as Batman, Henry Cavill as Superman, Gal Gadot as Wonder Woman, Jason Momoa as Aquaman, Ezra Miller as The Flash, Ray Fisher as Cyborg, J.K. Simmons as Commissioner Gordon and Willem Dafoe an Atlantean, Nuidis Vulko.
Fueled by his restored faith in humanity and inspired by Superman’s selfless act, Bruce Wayne enlists the help of his newfound ally, Diana Prince, to face an even greater enemy. Together, Batman and Wonder Woman work quickly to find and recruit a team of metahumans to stand against this newly awakened threat. But despite the formation of this unprecedented league of heroes—Batman, Wonder Woman, Aquaman, Cyborg and The Flash—it may already be too late to save the planet from an assault of catastrophic proportions.