The correct answer is C. 6.
There are 2 female members in the nuclear family: the mother and the unmarried daughter. There are 6 female members in the extended family: the mother, the unmarried daughter, the 2 daughters-in-law, and the 2 granddaughters.
Option A is incorrect because it only includes the mother and the unmarried daughter. Option B is incorrect because it only includes the mother, the unmarried daughter, and the 2 daughters-in-law. Option D is incorrect because it includes all of the female members in the family, including the mother, the unmarried daughter, the 2 daughters-in-law, the 2 granddaughters, and the wife of the son with a son.