What does "hard angles" mean when describing a person's character?

I'm reading this novel, and there's a passage I don't quite understand. It describes a heroine's character, and goes as below:]

She is a smart, gorgeous chameleon, all heart and hard angles.

Specifically, I can't figure out what "all heart and hard angles" mean. Can someone please help me?

Solution 1:

I think it refers to chameleon part of the sentence, which means instability of the character. So she sometimes can be all heart (kind and caring) and sometimes - all hard angles (cold or even hostile).

I would describe this all heart and hard angles as tsundere type of person.