"She's got life under her skin"... what does this phrase mean, metaphorically?

Answer 1

simple, its like the old saying "don't judge a book by it's cover. "she" may appear to be something she is not. maybe mean? but she's really not, there's always different feelings lurking within the person who neglects to show them. As goes for the class bully who is dumb, he's upset and angry at life for a reason but he takes it out on everyone else.

Answer 2

...she's got fire in her bones. You dare her and she'll steam u to boiling point.