Although she was beautiful, she was also modest and did not draw attention to herself best summarizes the meaning of the poem's second stanza.
A violet by a mossy stone
Half hidden from the eye!
She was beautiful like a violet, nevertheless a mossy stone does not allow one to focus on the violet. A violet is small and the attention would be on the mossy stone rather than on the violet. This a metaphor, she is a violet.
Fair as a star, when only one
Is shining in the sky.
She is beautiful like the star, this also means her beauty enlightens the place. This is a simile: fair as a star.