А вот Lady или Mistress - это, кстати, очень большой вопрос... Зависит от функций.
От Хозяйки Медной горы зависила вся жизнь в регионе, а Хозяйка Озера просто хранила его секреты и всё.
Так что она может быть и Mistress. Ср. характеристика Тома Бомбадила по Толкину:

"Frodo looked at her questioningly. “He is, as you have seen him,” she said in answer to his look. “He is the Master of wood, water, and hill.”
“Then all this strange land belongs to him?”
“No indeed!” she answered, and her smile faded. “That would indeed be a burden,” she added in a low voice, as if to herself. “The trees and the grasses and all things growing or living in the land belong each to themselves. Tom Bombadil is the Master. No one has ever caught old Tom walking in the forest, wading in the water, leaping on the hill-tops under light and shadow. He has no fear. Tom Bombadil is the Master".