I’ve got another one of those puzzlers for y’all.
I would have read it in the nineties, but I think it was a bit older than that. The protagonist was a teenage girl. The whole thing was set in fantasy-ish world where I think there was no sun; I think it was blocked out by smog. The protagonist was part of an undercaste that I think mined coal. She had some sort of power that could generate heat or fire or something like that and she was picked up by some male noble who noticed. I think he was about her age. The main thing I remember is that her family’s symbol was a stylized lion head, but we find out in the end it was really a sun disc.