Reference: Fataawa Noor ‘alad-Darb – Volume 11, Page 77, Question No.5624
Question: What is the ruling regarding women leaving their nails to grow long; is that permissible?
Response: Men and women who leave their nails to grow long, are in opposition to the natural disposition upon which Allaah created mankind. And the Prophet (sal-Allaahu ‘alayhi wa sallam) has stipulated for his ummah not to leave the trimming of their nails, moustache, pubic hair and armpit hair beyond forty days – and this has been authentically reported from the Prophet (sal-Allaahu ‘alayhi wa sallam). So both men and women should not leave their nails to grow long, and certainly not beyond forty days.