lack of protein can cause growth failure, loss of muscle mass, decreased immunity, weakening of the heart, weakening of the respiratory system, hair loss in some and feeling weaker in general. protein malnutrition can lead to things like kwashiorkor too. it can contribute to other pretty bad things in future too.
as you dont eat meat, eggs or cheese it would be hard for you to get sufficient protein. its best to get a minimum of a gram of protein per kilogram of bodyweight. its very hard to get the complete proteins containing all of the essential amino acids from vegan foods. try to eat fish as much as you can as you eat that, also try to buy tofu and maybe a soy protein supplement. tofu is a very high source of protein and very low in fat and tastes pretty good too. soy has other benefits too, it has been proven to help lower bad cholesterol levels, and even helping things like hot flashes and much more.
as for people recommending protein shakes, most protein supplements are whey protein which derives from milk and cheese (the things she doesnt eat). if you do buy a protein supplement, make sure it is a soy protein supplement which you should be able to obtain from your local health shop as it doesnt contain milk, cheese or any meat extracts.