Breast-feeding that prohibits marriage takes place at least five times during the first two years of breast-feeding. If your grandmother breast-fed you this way, you are a foster son to her and a foster brother to all her children. Hence, it is unlawful for you to marry your uncle's daughter because she is the daughter of your foster brother. Allah (Exalted be He) says:
Forbidden to you (for marriage) are: your mothers, your daughters
to His Saying:
...your foster milk suckling sisters
Allah (Exalted be He) also says:
The mothers shall give suck to their children for two whole years
It is authentically reported from the Prophet (peace be upon him) that he said:
Wet-nursing makes unlawful what consanguinity makes unlawful.
It is also authentically reported on the authority of
`Aishah (may Allah be pleased with her) that she said: (It was among the revelation of the Qur'an that ten known times of breastfeeding make the marriage prohibited, but this was later abrogated and reduced to five. The Messenger of Allah (peace be upon him) died and the ruling remained effective.)It should be noted that if the baby sucks the breast then leaves it, it is considered one time for him of breast-feeding and if he did it again, it will be considered a second time of breast-feeding, and so on. (Part No. 21; Page No. 27) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.