Dorea (Black) Potter (1920-1977)
Daughter of Cygnus and Violetta (Bulstrode) Black (BFT).
Three older siblings: two brothers Pollux (1912-1990) and Marius (disowned, dates unknown), one sister Cassiopeia (1915-1992) (BFT).
Married to Charlus Potter; they had one unnamed son (BFT).
It is doubtful that Dorea is Harry's grandmother because Jo has told us that "James's parents were elderly, were getting on a little when he was born, which explains the only child, very pampered, had-him-late-in-life-so-he's-an-extra-treasure, as often happens, I think. They were old in wizarding terms, and they died." (TLC) Dorea was only 57 when she died.