The heroine is a reluctant frontierswoman of the 1880s named Catherine Crocker.
From the time.com
Calamity Jane, notable pioneer frontierswoman and scout, at age 43.
From the en.wikipedia.org
While Eva's transformation from pampered European cosmopolite to Wild West frontierswoman might sound outlandish, her story is, as a matter of historical fact, not all that unusual.