if she can keep her grades up and is active in church out in the mission field, her chances to get accepted increase greatly. My son was accepted to BYU because he spent most of his youth living in Sweden. Even though we had moved to Utah his foreign status I'm sure played a huge role in getting in. Of course it helped that he was a star student and had already finished his Associates at Weber State before he graduated from High School.
I am convinced that the admissions when all things are equal will want those youth who have not had the benefit of the LDS resources and environment that is available in Utah and surrounding states to enjoy that experience as a student. After all, what is the main purpose of BYU?