She needs to gradually up her mileage. She has NO base. Some runners can run somewhat good off of only 30 miles a week, but that is the exception. As a 15 year old, she can slowly build to 40 miles a week. This will help her immensely. I agree with the poster who mentioned tempos. In winter and summer base, the majority of the hard efforts(2 a week) need to be at threshold effort. This could be done with 3 mile tempo runs, 4-5 X 1000m repeats at threshold pace, or fartleks. She also needs a long run. The rest of her runs should be at an easy pace, with strides. Once the season starts, do not forget about threshold efforts, especially if focussing on the 5k. If she does this, her mile time and her 5k will drop a lot.