Mike,
I have no first-hand knowledge of how it works in Vietnam, but in the Philippines you are not allowed to send her a ticket. It must be printed in the Philippines…probably a trade protection thing for their travel agencies? There is also a special travel departure tax included in the ticket price that many stateside ticket sellers are unaware of.
Why don’t you have her check some ticket prices with some local travel agents over there? When my wife first flew over the best price for a one-way ticket that we could find was with a local travel agent in the Philippines. They were able to check the prices for all dates in her requested range and found a great deal with Cathay Pacific that also had the easiest connections of any airline. The travel agent handled everything including tips on customs restrictions, and I think they even had an accurate scale to let her pre-weigh her bags to make sure they didn’t go over the weight limits.
This was the easiest way to do it for the wife because she had the most control over her travel plans. I just sent her the money and she took care of the rest.
Another option is to purchase through an airline or ticket agent that has an office in Hanoi. That way, you could pay here and they could issue the ticket to her in person at their local office.
Some airlines have an E-ticket option but I think I would be leery to send her to the airport with one of those on departure day, taking a chance that there might be any last minute problems to screw thing up and put her under even more stress.
Ray