An analogy is a comparison of two things that may be quite different from each other, but the statement explains that idea or thing by comparing to something familiar. Therefore, the only complete idea is the second option:
My cousin is like a whirlwind; she arrives out of nowhere, leaves a mess, and disappears.
Because the author is trying to say that his cousin does not behave well, he always makes a mess in the house and then instead of cleaning the disaster he made, he leaves. Then it is easy to find it similar to a whirlwind, because it is also unexpected and causes a disaster that someone else has to clean.
