Uh, since you did not open the package, I would guess it has nothing to do with you.

A rosary is the last thing I would be afraid of, or associate with scary things. Maybe it means the sun will shine special for your sister? Maybe it was found with the package, and somone put it inside thinking it fell out. Maybe right now another message board is filled with speculation on "what could have happened to that rosary?" "I wonder what it means?" "I'll bet someone was so sinful the rosary could not handle it, and it jumped into a random package at the post office."