Mary Shelley's Frankenstein is a Romantic-Gothic text. The language of the text is eloquent and beautiful. As part of the vivid images provided by Shelley in the text, she also includes numerous literary/rhetorical devices.
Although typically found in poetry, alliteration can be found in the text. Alliteration is the repetition of a consonant sound (again, typically within a line of poetry). For example, Big brown bear batted at biting black beavers. The repetition of the "b" sound is alliteration. "From a flourishing state, fell," from chapter one (paragraph two) is alliteration.
He strove to shelter her, as a fair exotic is sheltered by the gardener, from every rougher wind.
In the above quote appears a simile. (A simile is a comparison between two typically dissimilar things using "like" or "as.") In this sentence, Victor (actually Walton) is retelling about how Victor's father sheltered Victor's mother--as if she were an exotic flower needing protection. Therefore, the sentence compares Caroline Frankenstein to an exotic flower.
The sentence also contains a metaphor. (A metaphor is a comparison between two typically dissimilar things, not using "like" or "as.") Victor's father wished to shelter Caroline from "every rougher wind." Rougher wind refers to any challenges she may face in life. Victor's father thought that Caroline had already lived a trouble-filled life and needs to face no more strife. Therefore, the metaphor exists in the comparison between trouble and rough winds.