I can't remember the name of this book I read years ago!?

I don't remember who wrote it or what exactly the title was. The cover of the book had this teenage girl with blonde hair or red hair in a dark cloak with a hood on. She had her hands in front of her and she was holding a stone that was glowing orange. I think the title was The stone of cold fire or the coal of fire...something. She was a slave working in a coal mine and came across that stone. I think it had magical powers and she was the only on that could harness them. I don't remember much else. I think she ran away and ran into some lumberjack guy but he ended up being a bad guy. Please help me find this book. It's killing me that I can't find it. I can't remember much more. If I do, I'll add to the post to help you out. Thanks in advance!