The Truth About Everything, by Bridget Farr

Lark lives with her parents in a remote homestead in Montana.  Until the age of fifteen, she thinks that she's learned everything she needs to know.  She can hunt and fish, repair engines, and defend her family from the government.  But when she gets her first period, she doesn't know what is happening to her.  She thinks she's miscarried like her mother did with each of her pregnancies (except Lark).  It sets Lark wondering that there is a lot else she hasn't ever learned about.  Like how to read.  Like what really happened on 9/11. Like what normal teenagers do with themselves.

No longer content to stay sequestered in the family's remote fortress preparing for the Armageddon, she secretly enrolls in school and develops a longing for knowledge.  And the more she learns, the more she realizes the limitations of her parents and the way that their paranoia is killing themselves and her.

A grim story of a wildly abusive family.  I'm not a big fan of child endangerment, but I am inevitably sucked in by stories like this.  For as unpleasant as the setting is, I long for watching the child rise above their situation.  Lark doesn't disappoint.  She has a lot of handicaps, but her survivalist parents got one thing right:  making her intensely curious and fiercely independent.  So, for every time I cringed at her Dad's stupidity and her Mom's cowardice, I could still cheer at Lark's tenaciousness.  That's small comfort in a story that will just depress you and leave you wondering how many Larks there are out there and what happens to the ones who lack Lark's survival skills?