One More River — Lynne Reid Banks

"WE'RE GOING TO EMIGRATE"
The words dropped into Lesley's mind innocently...and exploded like a bomb. Emigrating meant leaving home forever. She couldn't believe it. But her father had made up his mind.

"WE'RE GOING WHERE WE CAN LIVE ON AN EDGE...WITHOUT CHALLENGES, WE ROT, MIND, SOUL, AND BODY."
Life on a border Kibbutz in Isreal turns out to be one challenge after another for Lesley, who has always taken "the good life" for granted. At home she was popular, successful at school, and trendily dressed. Now it's all gone. A stranger in a strange land, she has to start from scratch, and that includes learning a new language, doing manual work and sharing sleeping quarters with three others -- one of them a boy.

And just across the river Jordan she can see the enemy.

Lesley doesn't think she'll ever adjust, or that she even wants to. But that's before the ultimate challenge of a full-scale war brings her to a new understanding of her family, her people, and herself.