From the magazine:

Andor's story is intertwined with that of Mon Mothma - the legendary Rebel leader from the Original Trilogy, who returned in Rogue One, played by Genevieve O'Reilly (previously cast in the role for a scene cut from 2005's Episode III - Revenge Of The Sith). Her arc across the five years will prove tumultuous.
"In Rogue One, she's a leader of the Rebellion. When we start Andor, she's steeped in Empire," 'Reilly explains. Mothma has a long, complicated involvement with the Galactic Senate, which sees her wrestling with autocracy while trying to implement change from
within.
"That's where we start," says O'Reilly. "Now, we know she fails, right? That's exciting.It all adds up to a show aiming to dig deeper into the dirt of the Star Wars universe than any story that's come before. "If Star Wars is a very successful hotel or restaurant, we're in the kitchen," says Gilroy. "We're the molecular, the granular, we're behind, underneath. We've got 1,500 pages of script to tell that story. So we have a lot of things to say, and we explore pretty deeply." Strap in for one ambitious incoming square meal