1) I second the recommendation for not restricting your caloric intake to 1800. Your body will go into "starvation mode" which means it will store every calorie into your fat cells, thus making you gain weight.
2) You need to exercise or lift more. Thus your diet needs to reflect that change. Make sure you eat enough protein or else your cardio will destroy the muscles you build up.
3) As for food, pick something healthy and something that YOU like. It is also better to eat 5-6 small meals a day and not to eat anything big before bedtime. Take snacks with you to class like almonds, carrots, apples, whole wheat crackers, meal replacement bars, etc along with a bottle of water. You should also do this in the library or where ever you study. Eventually this eating schedule will turn to habit and it won't be as difficult. (note, when you do bring food to class make sure it doesnt have a strong smell, make a lot of noise when eaten, and too messy for you to type or take notes).
4) Finally, remember to do experiment and pick a lifestyle that works for you. No one here can tell you what is the best diet/exercise program that is best for you. Create your own program and if you fail pick another one and make your adjustments. Yes it is hard to balance your health with your life and law school, but it will only get worse once you start working in a law firm. Remember that this should be a lifestyle change and not just a short-term diet/exercise program. Good luck and happy living!
I don't consider 1800 starvation. I know girls who try to restrict to under 1000 and they can only maintain it for a day or two. I have found if I drink water only 1800 is no problem. Most of the government websites seem to be of the opinion that if you consistently take in less than the numbers they provide, your body will not adjust and you will lose weight. Of course, this is the government we're talking about.