Take another look at the sentence:
If you offer Valerie a piece of watermelon, she will refuse it, the slices look like the wicked smile of a circus clown who once scared her as a child during a trip to the big top.
No problem exists between her and as. As a child during a trip to the big top is a string of three prepositional phrases. When you connect prepositional phrases to the end of a sentence, you generally do not need punctuation.