Given her daughter's recent birth, Miller -- who welcomed Marlowe in her native London -- was unable to attend the panel with director Julian Jarrold, 51, actress Tippi Hedren, 82, and actor Toby Jones, 45. (The Girl explores Hedren's relationship with famed filmmaker Alfred Hitchcock during the making of the 1963 classic The Birds; Miller plays the part of Hedren.)
Us Weekly first broke the news of Miller's pregnancy in January, though she waited to confirm the news herself until asked about it in the April issue of British Vogue.
"I'm in my second trimester, so I'm I-can-talk-about-it pregnant," the notoriously private star told the fashion magazine. "Even though I'm under strict instructions not to say anything as it would completely defeat the point of everything I've tried to achieve in the last eight years."