I too am a 120 pound Div 1 female runner who runs 40 to 50 a week (800 runner). I am 5 foot six and my goal is 115 as well which is what I weighed 6 months ago when I wasn't injured. 115 is my race weight and the extra 5 really slows me down. What works for me is just eating CLEAN. Veggies, fruits, whole grains. I ONLY drink water for fluid intake. Juices and beer are empty. You should be getting your calories from solid food. But every once in a while, hey its OK to have your cake and beer :)
My healthy eating plan:
breakfast- 1/2 of it should be carbs, 1/4 should be protien 1/4 should be fiber (1/2 cup oatmeal with raisins, banana, 2 eggs for example)
Lunch-1/2 protien, 1/4 carbs, 1/4 fiber (apple, sandwich with turkey and veggies, cliff bar for example)
Dinner- 1/2 fiber, 1/4 protien, 1/4 carbs (1/2 cup cooked brown rice, chicken breast, large plate of veggies for example)
And of course, snacking and post-fueling your run is nice with nuts, chocolate milk, something to recover with.
The diet examples above obviously can vary. Get creative with what you eat and not the saaame thing everyday or it gets boring. I am always satiated when I eat this way and always lean up. Keep portion sizes appropriate, make sure you aren't starving, and eat healthy!
I would advise losing 1 pound a week as you are already small. Losing 2 a week may fatigue you and affect your runs.
Good luck!