Figures of speech in "Three years she grew in sun and shower" would include simile and metaphor.

We can observe a simile in the third stanza of the poem, where the speaker says that Lucy will be "sportive as the fawn." A simile is a figure of speech that compares two dissimilar things using the words as or like. Lucy isn't a fawn; she's a human being. But by comparing her to a fawn, the speaker is saying something about her character and her personality.

The simile also highlights the tragedy of this young girl dying at such a young age. She had so much life and vitality left in her when she was so suddenly and cruelly snatched away by Nature.

Lucy is also compared to a flower: "a lovelier flower / on earth was never sown." This is a metaphor, which, like a simile, involves a comparison of two distinct things, but without the words like or as. It is because Lucy is so beautiful, as beautiful as a flower, that Nature wants her for itself.