Her name was omitted from the first draft of the press release, but now Keri Russell is officially part of the Star Wars: Episode IX cast. Disney amended the cast list on the press release and put the updated version on the official Star Wars website.
You can see the revision below.
“Returning cast members include Daisy Ridley, Adam Driver, John Boyega, Oscar Isaac, Lupita Nyong’o, Domhnall Gleeson, Kelly Marie Tran, Joonas Suotamo, and Billie Lourd. Joining the cast of Episode IX are Naomi Ackie, Richard E. Grant, and Keri Russell, who will be joined by veteran Star Wars actors Mark Hamill, Anthony Daniels, and Billy Dee Williams, who will reprise his role as Lando Calrissian.”
Star Wars: Episode IX, now officially featuring Keri Russell, begins production August 1.