1978 (aged 18)
Mirabelle Scheer was a Halfblood Witch and a Mooner. She attended Hogwarts School of Witchcraft and Wizardry from 1971-1978 and was sorted into Gryffindor. She was diagnosed with Mooney Madness in 1976, and died of it only two years later.
Mirabelle is a French name derived from Latin mirabilis "wonderful". This name was coined during the Middle Ages, though it eventually died out. It was briefly revived in the 19th century.