Hello,
First of all allow me to command you on supporting your daughter in her decision. That's quite fantastic!
I have been a vegetarian for 9 years now and as of my last check-up I am in great health, even my iron and B-12 are good (those two are the main concern for those who are on a veggy diet), so I am pretty confident that I know what I'm doing by now.
As someone previously mentioned eating too much pasta is not a good way to go. For vegetarians or otherwise. It's yummy but really has very little nutrition.
Grains are your friends. There are a lot of them (rice, buckwheat, quinoa, barley, cous-cous) and most of them pack a great variety of nutrients. You can find them in quick to make variety and the takes-forever-kind so make sure to read the preparing instructions.
Green leafy vegetables. The darker the green the more nutrients. Iceberg lettuce "026 not so great. Spinach? Fabulous! That actually applies to all coloured veggies. The deeper the colour the more nutrients it contains.
Nuts. All kinds of nuts, if she is not allergic they are great for snacks and to throw into a salad. Same with dried fruit and berries.
Now-a-days there are a lot of substitutes for meats available. My fave are mock chicken and mock fish. Some Asian supermarkets have great meat substitutes in the frozen food isle, like mushroom "lamb". Even my non-vegy friends absolutely love that stuff.
Since you said vegetarian I will assume she will still eat eggs and dairy. In that case eggs are a fantastic source of protein and vitamins/minerals.
The recipes she will choose to use will really depend on what she likes. The best thing is to try to include a wide variety of foods in her diet. What I usually do when I don't have much time or motivation to spend in the kitchen is make buckwheat (takes about 10min), a quick salad with my fav veggies (cucumber, tomato, spinach, green onion, bell peppers, etc) and then fry up some vegy chicken bits with a bit of sauce and one egg. (This also takes may be 20 min all together) Quick delicious and great nutrition.
One thing your daughter will probably notice is that she gets hungry faster so make sure she know to have some healthy snacks on hand. Peanut butter/banana sandwiches are glorious!
The main nutrition concern she will have is getting enough iron and vitamin B12. Those two are almost impossible to find in non-animal products. She will most likely need some supplements. My fav so far is Noni fruit powder for iron (you gotto be careful not to overdose but it is rather wonderful).
Anyway, sorry for blabbing for so long, but i get a bit excited when someone joins this lifestyle and I wish for them to succeed, feel great and be healthy. Hope the above helped even if a little. Cheers!