You caught your sister, the one who usually gets away with murder, doing something awful. Unforgivable. Do you tell on her or do you smack her around to teach her a lesson?

I always have my sisters back...even if we don't get along

They smacked me around a lot and then ratted me out to Mom.

Nothing.
If she gets away with murder, wouldn't I just be wasting my time...saying/ or doing something?

I don't have a sister, but I always took the blame (and ass whoopin) for what my younger brother did.