Hattie Big Sky by Kirby Larson 289 p.

When sixteen-year-old orphan Hattie Brooks finds out that her uncle has left her his Montana homestead, she can't wait to take it on. When she arrives, she discovers that to keep the land she must cultivate 40 acres and set 40 rods of fencing in the next ten months AND pay off her uncle's debt.  The hardships of life on the prairie are tougher than Hattie expects, but she perseveres, making friends with her neighbors, asserting her independence, and often recording her ups and downs in letters to a good friend fighting in France during World War I.