Is it permissible for me to propose to my maternal aunt's daughter, who is six months older than me, given that her mother suspects she breastfed me once, and knowing that my maternal aunt is my mother's sister through nursing?

Prohibition is not established by doubt concerning the original act of suckling or the number of sucklings. Therefore, marriage to a maternal aunt's daughter is permissible in this case, though it is preferable to avoid it as a precautionary measure.