She 'went into mourning' for her dead husband. [=she began to mourn for her dead husband]
She is still 'mourning' her husband, who died last year.
She is still 'in mourning' for her dead husband.
(..) We never talked about Tommen. There's nothing to say. Our baby boy killed himself. He betrayed me. He betrayed us both. Should we spend our days mourning the dead... Mother, father, and all our children? - Cersei... - I loved them. I did. But they're ashes now and we're still flesh and blood. (..)2017 TvShow: Game of Thrones Title: Dragonstone Season: 7 Episode 1