Did your friend use a Vietnamese agency? Does your friend actually have a ticket issued (as in, does she have ticket numbers) or did the agency just reserve her seat?
I ask because Viet agencies everywhere are notorious for claiming that the tickets were issued when in fact they were just put in reserve, with the agency hoping to find a cheaper fare to keep the difference (with the passenger not knowing any better).
I'm betting their reluctance in changing the name is from their being afraid that your friend would find out their ruse.
If that's not the case, the travel agent is still wrong and your friend should continue to hammer them until they actually do it.
Good luck.