A metaphor is a figure of speech comparing unlike things by describing them as something else.
Metaphors are often used to help you clearly picture something. They use a linking verb like “is” or “was.”
It is an implied analogy or unstated comparison which imaginatively identifies one thing with another. This device is used by an author to turn or twist the meaning of a word. (enotes)
Since you said the person is pretty, I am going to assume you want positive images. I will begin with the acne. Acne is not usually considered positive, but it could be.
Her face was a strawberry of zits.
In this case, the pocked nature of a strawberry is compared to the acne. It’s still not completely positive, so you might consider replacing “zits” with “pimples” or a less offensive word.
Frizzy hair is also not considered good usually. If you want to make a positive image, think of something positive or good that’s frizzy.
Her hair was cotton candy.
You can also use a simile to say her hair was “as frizzy as cotton candy” if you like.
Finally, she is smart and pretty. You have tried to imply that she is pretty before. You can combine these two by describing something you find pretty and smart.
She was a shiny new apple computer, smart and pretty.
Of course, something that is pretty and smart is up to you, but you get the idea.