Earth is a danger to all of the Universe, so some Federation of civilizations sends a glowing, radioactive woman to, well, interfere with a kidnapping. She touches the bad guys and they fall down dead from radiation poisoning.
The title of this whopper is so much better than the actual story: The Astounding She-Monster (1958).
Oh, and we get to the end of the movie, and the message left by the alien is … “Come join our Federation.” Wait, what? Continuity!
Oh, this was dreadful. Please do not waste your life on this one.