Accounts of Mithrellas's early personal life is not known and is partially veiled in legend, but around 1980 3A, she had become lost in the woods of Belfalas and was found by Imrazôr, the Númenórean. He took her into his household, fell in love with her and became her husband. She bore him a son, Galador, who later became the first Prince of Dol Amroth, and a daughter, Gilmith.
Mithrellas was a Sindarin word of unknown meaning. There appears to be many possibilities to the origin of her name, including mith, which can be interpreted as both "grey" and "mist", rein, renia or revia, which can be interpreted as "wandering", "track" or "sail", and las, meaning "leaf" (especially pertaining to trees).
If these words were to be the origins of the name Mithrellas, it could possibly, and rather unusually mean "wandering leaf of the mist" or "wandering grey leaf", though it is unlikely.