It is not permissible for a woman believing in Allah and the Hereafter to observe mourning on the dead for more than three (days), except in case of her husband.
عَنِ النَّبِيِّ ﷺ قَالَ لاَ يَحِلُّ لاِمْرَأَةٍ تُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الآخِرِ أَنْ تُحِدَّ عَلَى مَيِّتٍ فَوْقَ ثَلاَثٍ إِلاَّ عَلَى زَوْجِهَا