We think of these books as memoir/autobiography, but in reality they are fiction. Which is to say that, although the bones of the story are likely true, they were likely embellished. Which is perhaps a good thing, when it comes to the book The Long Winter. I've lived in South Dakota in the winter, and I am quite sure that the winter she writes about was long! (And they didn't have central heat, either.) But my friend pointed out to me a couple of years ago that (despite the fun depicted in the cover illustration) The Long Winter is essentially a tale of near-starvation. I went back to the story and re-read it, and when read that way, it is breathtakingly scary.
Update: I just took a look at the Wikipedia entry for The Long Winter (should have done that first!) and it says:
The Long Winter runs from the fall of 1880 to the spring of 1881; a season of such frequent blizzards that it went down in history as "The Snow Winter". Accurate details in Wilder's novel include the names of the townspeople (with only minor exceptions), the length of the winter, the Chicago and North Western Railway closing down business until the Spring thaw, the near-starvation of the townspeople, the severe cold, the terrible danger of getting caught in a blizzard, and the courage of Almanzo Wilder and Cap Garland, who ventured out on the open prairie in search of a cache of wheat that no one was even sure existed.
The fictionalized material includes the "Indian warning" in an early chapter and the nonstop procession of blizzards lasting on average three days each, with only two to two-and-a-half days between them from late October until early April.