Harriett Wingfield was one of Vivian Wingfield's younger sisters.
After graduating from Hogwarts, she and Nancy were each forced to fight a dragon in order to earn their Wingfield name. When it was Harriett's turn, she was overpowered by the dragon and almost killed. Nancy disobeyed their father and defended Harriett, at the cost of her own life.
Harriett was disowned by her father and the Wingfield family. There are conflicting reports on what happened afterwards, but it is known that she eventually committed suicide.