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

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.