Breastfeeding from the grandmother who is old and has no milk
If the situation is as you have mentioned, that the grandmother who breastfed you had no milk in her breasts, it is permissible for you to marry your mentioned cousin. However, you must be sure that your grandmother had no milk in her breasts, either by asking her if she is still alive, or by asking those who knew her at that time, in case
the breastfeeding took place five times or more during the toddler years. However, if it was less than five times, it does not prohibit marriage, according to the Hadith narrated by
`Aishah (may Allah be pleased with her) who 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."
(Part No. 21; Page No. 49) If the breastfeeding takes place after the toddler years, it does not prohibit marriage, according to Allah's saying,
The mothers shall give suck to their children for two whole years, (that is) for those (parents) who desire to complete the term of suckling
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.