Answer: her inner goodness.
In Lord Byron's poem "She Walks in Beauty," we read the description of a very beautiful woman. Although for most of the poem Byron seems only interested in her physical appearance, he does not claim to love her, or even know her. Moreover, in the end, he remarks on the beauty being a mark of her "innocence." This shows that the beauty is not a lustful characteristic for him, and instead, it is a reflection of the woman's purity and goodness.