What is a good story for a large scar on your face?

I'm writing a story (suppose it qualifies as short story but it's probably going to end up 150+ pages) where the most appealing aspect other than the plot itself is how realistic all the characters are, with very complex and very different personalities. This is a huge part of what makes the story awesome. = )

Anyway, I need to give one of the female characters a scar, somewhere hard-to-hide like her face. But I have a touch of writers block in this one area; I can't decide what kind of scar (laceration, burn, etc) and a good story for how she got it.

She has excellent martial arts skills, but uses no weapons, and the rest of her backstory is a riches-to-rags tale. She is mentally unstable due to her incredible fall from grace and acquired the art as a means of self-defense from most other homeless persons. It would be great if there was a way she got the scar from when she was in her position of power, so I could use it as a hint before I reveal that fact. Or maybe from something that happened during the revolt against her. She had almost-goddess-like status (there were small groups who thought of her as a higher being) but upon discovering the side effects of said power there were several attempts on her life and she was helped to fake her own death. This all comes to light the first time she answers a question about the scar.

What is a good, visual cue to someone's violent past like that? If it weren't for the scar she would be very pretty and her demeanor is that of a queen. The scar needs to directly contrast that.

Cool scar stories, anyone?

Creative help and real-life experiences are very much appreciated. Thanks for reading! = )