Unmarried spouse visa

Best thing to do is check with the Viet Nam embassy.  You can also search online to see the different types of visas.  You can start your search with http://vietnamembassy-usa.org/consular_services/.

While I can not speak for Vietnam directly I can say that unmarried spouse visa are always difficult.
You have to be able to prove the relationship and while this may appear easy, when you start trying to collate evidence you will be amazed at how little you have that actually proves you are a couple.
You will need evidence such as utilities bills in both names, bank accounts any other legal documents etc... Transcripts from witness etc photos (although some\most places are reluctant to accept these).
as has already been said talk to the VN embassy in your home land and ask them what is needed.
hth

Hi. I think either you need to get married or she needs to get a job offer in her own right. Or she could offer to be a volunteer English teacher in an orphanage. Otherwise she can only get a tourist visa for one month which she can extend to three months once there. That's what I think, but do check the Vietnamese Embassy website.

Thanks all.

@maggiebones - yes, that's what my research is showing too. 

Looks like I'll just have to make an honest woman out of her before too long.