How wonderful of you, and yet how sad it must be for the child. My advice to you is to play, read books, color, sing, do things that she likes to do; it's in the doing that language blossoms in 5 year olds. Talk with her as much as you can in both Korean and English. If you have friends, non-Korean, and females yours age, that wouldn't mind spending time with the child, that too wouldn't hurt.
As for the pyschological aspect, the teachers at the schools are trained and experienced in these situations. It's imperative that the child be able to learn to adapt to her new surroundings. This is a serious issue from what I can tell.