Thinking aloud, I'd be inclined to book a fully refundable one way ticket back to Vietnam a year out then cancel it when she gets here. This way you wouldn't have to worry too much about people needing the return ticket (though I don't think it's required for the super visa anyway from what I read about it when it was in the news not long ago). Best I could suggest is figure out where she will transit then give her a letter in the right language where she is transiting that explains everything and includes your phone number; if she gets stuck she shows that to customs people.

Finally, does she have a smartphone with google translate? This can also help a lot - can google translate do Vietnamese?

Either that or use points to go meet her at the transit point.