Miriel was the first wife of Finwë and the mother of Fëanor. After giving birth to her son, she wished to die, an impossibility for one of the Eldar, what with the whole immortality thing. She went to the gardens of Lórien in Valinor, where she laid to rest and her spirit left her body of her own free will. Understandably, the Valar and the Eldar found this to be really weird.
Her husband, Finwë, remarried, much to Fëanor's chagrin.
You might also be looking for Tar-Miriel (Ar-Zimraphel), who was the last Ruling Queen of Númenor (at least until her crazy cousin Ar-Pharazôn usurped her throne, married her, then installed Sauron as his most trusted adviser.