Why is Jenny considered an unreliable narrator in The Return of the Soldier? How does the narration make it a modernist text?

The limited point of view of Jenny's narration makes Rebecca West's novel The Return of the Soldier a modernist work; the third person narration Jenny offers does not include the thoughts and feelings of other characters, except for what Jenny observes and assumes. Because this style of narration depends entirely on one character, any biases or prejudices she might hold transfer to the reader. Jenny's unreliability is not necessarily a criticism of her character, but it is a natural outcome of the narrative technique West has chosen to employ while telling this story.
For example, Jenny has her own feelings towards Chris and Kitty and Margaret, feelings which reflect only her own experience and impressions of the other characters. She doesn't say much about Chris specifically, so the reader must gather conclusions about his character, and she is snobbish about Margaret at first, so the reader only receives impressions of Margaret that reflect class differences. As well, Jenny's understanding of Kitty is also limited. All of these limitations make the text a modernist one, full of Jenny's authentic humanity and imperfection, rather than a reliable one.