Helen
Inkling
But surely we're straying from the definition of 'mentor', then. I mean, a young child in a story could be the one who teaches the hero an important moral lesson, or even turns their whole outlook around and so on... but I wouldn't classify that role as a 'mentor' at all.
She certainly doesn't look like a mentor.
But the more you analyze her role and her influence on the change, the more she starts to look like one. She's more than just the romantic interest.
But my general point is that it's not what the character looks like but what they do that defines their archetype.