I have no help I'm sorry, but I just wanted to say how awful the sitution is!
The poor little girl shuttled back and forth between Korea and Australia, away from the family who love her and want her, and your SIL & BIL wanting her and not legally able to keep her!

There must be SOMETHING out there that could help with this sitution? What about a children's amnesty group? If they can gte someone on side to help them it may be easier.

Hope it all gets sorted out soon and she is able to join her family and start her new life as an Australian!