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.
(..) Mrs Clifton. You'll have to forgive us. We're not accustomed to the company of women. Not at all. l wss thoroughly enjoying my book. - The team is in mourning, darling. - Oh, really? l'm afraid we're not having much luck obtaining funds for the expedition. Oh. Well, what'll you do? (..)1996 The English Patient