She can't be cyrah. It's hinted that she has black hair. If you see cyrah's picture, she has amber sorta hair. I think it's tam and linh's sister or cousin at least. I don't think it's mai song, though. The book says she is 13~14 yrs old girl.
Plus if it was Shayda, she wouldn't have helped. And for Jolie, why would she fake her death? She could have slipped away.
And remember, the book says she is 13~14 yrs, doesn't it?