Breastfeeding makes forbidden what blood relations makes forbidden. Therefore, the breastfeeding mentioned in the question, five sucklings in the first two years, makes the women a [breastfeeding] mother to that child due to that breastfeeding. This is based on the generality of the Qur’anic verse,
'' [Forbidden to you for marriage are] your foster mother who gave you suck .” al-Nisa:23
Even if the milk was produced after she reached the age of menopause, the ruling is the same. If that women was married, the child would be her [foster] child and the son of the one whom the milk is ascribed to. If she was not married and produced milk, then she is the [foster] mother of that child and he has no foster father.
Do not consider it strange that one may have a milking mother and not a foster father. Also, do not consider it strange that one may have a foster father and no foster mother. An example of the first case is where a women gave two sucklings to a child, the milk that was the result of her first husband. Then she separated from that husband and married another after her waiting period expired. She becomes pregnant and has a child from her second husband. She then suckles her foster child again for the remainder of the suckling amount [with the milk that is the result of a child with the second husband]. She now has become that child’s foster mother due to the five sucklings but he has no foster father because he did not suckle at least five sucklings that were the result of one man with the women.
As for the second case, this is where the child has a foster father but no foster mother. An example is where a man has two wives. One of them suckles the child twice and the other suckles the child three times. In that case, he will be the foster child of the husband since he was breastfeed over five times from milk that was the result of intercourse with him. But he will not have a foster mother because neither the first nor the second women suckled him the minimum amount of times required.