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.
(..) One hundred and fifty dollars in gold. For what lady, sir? For Mrs. Charles Hamilton. For whom, sir? Mrs. Charles Hamilton. Mrs. Hamilton is in mourning, Captain Butler... ...but I'm sure any of our Atlanta belles would be proud to-- Dr. Meade, I said Mrs. Charles Hamilton. (..)1939 Gone with the Wind
(..) It was in the library. You had broken something. Yes, Captain Butler, I remember you. Ladies, the Confederacy asks for your jewelry on behalf of our noble cause. We aren't wearing any. We're in mourning. Wait. On behalf of Mrs. Wilkes and Mrs. Hamilton. Thank you, Captain Butler. (..)1939 Gone with the Wind