The Ruling on Marrying the Wife's Sister's Daughter After the Death of the Wife or (Marrying) Her Paternal or Maternal Aunt
Question :
Is it permissible for a man whose wife has died, to marry her brother's daughter, or her sister's daughter or her paternal aunt or her maternal aunt or their daughters?
Answer:
It is permissible due to the loss of the cause of the prohibition, which is combining two close relatives, which leads to the cutting of family ties. So if a man divorces his wife, or she dies, her sister, her brothers daughter, her sister's daughter, her paternal aunt and her maternal aunt and the daughters of the aforementioned become permissible for him.
Source:
Ibn Jibreen
Fatawa Islamiyah, Vol. 5 Page 227