Running out of Time. It's about a girl who think she's living in 1840, but it's actually 1996 and children are dying in her village so her mother tells her the truth that it really is 1996 and she sends her out into the world to get help.
This is the book that The Village movie was copied from. I got it for my daughter and I ended up reading it. It goes very fast.
by Margaret Peterson Haddix
http://www.amazon.com/Running-Out-Time-Aladdin-Fiction/dp/0689812361