Women who are forbidden in marriage in Islam because of kinship are: 1. The mother, which includes grandmothers on both the father’s and mother’s side. 2. The daughter, which includes granddaughters. 3. Sisters, whether full sisters or half-sisters through the father or mother. 4. The paternal aunt, which also includes the paternal aunt of the father or mother. 5. The maternal aunt, which also includes the maternal aunt of the father or mother. 6. The brother’s daughter, which includes his granddaughters. 7. The sister’s daughter, which includes her granddaughters.

A mother-in-law is permanently considered a Mahram to her daughter's husband, making marriage between them strictly prohibited. This Mahram relationship is established as soon as the daughter’s marriage contract is completed and remains valid even if the couple divorces or the wife passes away.