It is permissible for a woman to mourn for someone other than her husband for three days
Question

                I heard one of the scholars say that someone other than the wife is permitted to refrain from adorning herself and wearing her best clothes for three days in mourning for the deceased. How correct is this opinion?.
Praise be to Allah.
    This is correct, and it is mentioned in a saheeh hadeeth, in which the Prophet (blessings and peace of Allaah be upon him) said: “A woman should not mourn for one who has died for more than three days, except for a husband, four months and ten days.” Saheeh – agreed upon. End quote.