How we cite our quotes: Volume.Part.Chapter.Paragraph
Quote #4
If ever sorrow and suffering set their profaning marks on the youth and beauty of Miss Fairlie's face, then, and then only, Anne Catherick and she would be the twin-sisters of chance resemblance, the living reflexions of one another. (1.1.13.26)
This idea of a "twin-sister of chance resemblance" and the concept of "living reflections" pretty much sums up the book's identity theme. Identity isn't very stable in this book, and reversals, doppelgängers, and chance can alter it.
Quote #5
But resolute, clear-minded Miss Halcombe, was the very last person in the world whom I should have expected to find shrinking from the expression of an opinion of her own. (1.2.1.50)
Mr. Gilmore introduces an interesting question here—whether or not you can ever really know another person and predict how they will behave. In the world of The Woman in White, the answer is "Nope. Everyone is mysterious."
Quote #6
He could only assume that the intensity of Miss Halcombe's suffering under the loss of her sister had misled her judgment in a most deplorable manner; and he wrote her word that the shocking suspicion to which she had alluded in his presence was, in his opinion, destitute of the smallest fragment of foundation in truth. (3.1.1.7)
Laura's loss of identity has pretty widespread effects. Walter and Marian are altered by their connection to Laura, and the rest of the world pretty much thinks they're nuts. The diction here is worth noting: lots of big words and almost legal lingo, which is Walter's way of dealing with an emotional situation.