The shadow of a cloud moved across the field of grain and she saw the river through the trees. Hemingway uses the image of a momentary darkness to suggest the woman's growing disillusionment. A similar shadow gradually develops over their relationship. That look of seeing into things, of seeing through a thing to something else, was in the eyes of the sheriff's wife now. Mrs. Peters sometimes appears to be almost supernatural.
Ellipses indicate, of course, that some unnecessary words have been left out of a quotation.
Note that when you quote just a word or a short phrase, no ellipsis is necessary. In general, if you have to change more than two items in a short quotation, it's better to find another way to write it. The new and supposedly improved Dee tells her mother that she doesn't have to use her new name, Wangero, if she prefers not to.