What's the title of this book?

Ok this was a Young Adult book I've read in seventh grade. I'm 22 now btw but it was really good.

It was about this girl who was living in the 1800s in the US and her brother got sick. Her mom told her that she was actualy living in the present and she was living in a 'biodome' like place. The mom helped her excape and the girl had to find someone to help her family before she gets killed by these assassins.

I know it's totally WTF but can someone tell me the title or the author at least, please?

Since ages 9-18 includes every book I've ever read, this is actually really goddamn hard.

9-12
The Jungle Book
A Wrinkle in Time (and sequels)

12-15
Pullman's His Dark Materials trilogy
Discworld
Foundation Trilogy
King Rat, James Clavell

15-18
The Grapes of Wrath
The Moon is a Harsh Mistress
Time Enough for Love
A Song of Ice and Fire series
Spin, by Robert Charles Wilson