Jaimie Alexander returns as Lady Sif in the Thor sequel film, Thor: Love and Thunder. Lady Sif was not in Thor: Ragnarok. She probably was off world when Hela took over Asgard. This would explain why she was missing for Ragnarok and the clash with Thanos.
Natalie Portman also returns as Jane Foster. Jane Foster will take over as Mjölnir as the Hammer Barer. Taika Waititi will direct.