Familiar foods?  

I mean Vietnam has like 20 or so McDonald’s spots. They also have KFC and Lotteria. There are a lot of chain spots that you will find in other countries that serve similar food but they will also have their own special menu options. 

Yeah, there are several chain places but there are also local spots that offer familiar foods too. It is just a matter of checking the general area. Where will she be staying?  

There are plenty of restaurants that offer food that you can make work if you are not a fan of local dishes. There are stores that stock food items that are common in most other places around the world as well. 

Just tell her if she has never been to Vietnam or any countries like it, to avoid street food. Even if it is something she knows she likes because a lot of people have bad reactions to the food. This is not because it is unclean but because their body is just not used to it. 

There are plenty of options that she will have and likely be good with. As mentioned, if there are too few options she can get some packaged items at the store. 

Just stick with food you know. You can make adjustments to dishes as long as you are kind about it and not rude. People in many areas are used to having people visit from other countries and are willing to make your experience eating at their restaurant more enjoyable.