21-year-old actress Mary Mouser is carrying on the "Karate Kid" legacy with her starring role in the recently-released Youtube Red Series, "Cobra Kai." Mouser plays Samantha La Rousso, the karate-fighting daughter of Daniel La Rousso, the original Karate Kid. Mouser has also appeared in ABC's "Body of Proof," CBS's "NCIS" and the CW's "Life is…