You asshat, you’re making it sound like she snaps her fingers in half.
Martial artists like Jackie Chan and Bruce Lee (and yes, fucking Ming-Na Wen, that beautiful badass) will build up their bone strength by repeatedly (and fairly gently) striking sand, gravel, wood and steel - this creates tons of microfractures in their bones (smaller than even a hairline fracture) so the bones will heal over again and make the bones stronger and denser with increased deposits of calcium.
This has to be done over long-ass periods of time, so the bones have time to heal, and none of the fractures expand into actual breaks.
Oh, and she’s doing precise-ass kicks in HIGH HEELS.