I ran for NCAA D1 team and I trained my sister to a NCAA D1 scholarship.
Here are my thoughts on how you can train more by feel.
The point of base work and long slow runs is to better prepare your body for the more intense tempo / high end runs. It is during the tempo / high end runs that you will become more fit.
Forcing these tempo / high end runs will have negative effects.
Easy runs as supposed to be easy for recovery reasons. Remember you are doing this base work only to prepare yourself for the tempo / high end runs. You want to be recovered for the days you run the tempo / high end.
You do not need any intervals now. And while intervals are good, a HS girl doesn't need them to be near top in the state. Master the high end / tempo runs and you will never have to do 400-800 intervals during XC.
You do not need to plan in your schedule for tempo / high end runs. On the days you feel good, squeeze down the last 25 minutes so that the last 5 minutes is at tempo pace. You can begin this run at 10 minute pace and it would be ok. If you don't feel good, then don't do a tempo run. If you feel good two days in a row, then do 2 consecutive tempo runs.
If you have a deep urge for intervals or tempo workouts, I would go to a football field and do 40 * 80 meter strides at tempo pace or something similar. Work on form and running relaxed. In my opinion, for someone who doesn't truly understand high end / tempo runs, this is the best way to get the similar end effects. Tempo / high end runs that are run too hard will not be good for you in October / November.
No need for a watch in the summer. Operate by feel. Do not measure how fast you are going on the tempo / high end runs. Run by feel.
If you need more info please ask.
To show the purpose of base work and training for racing. Bernard Lagat is low mileage now because he has already prepared his body for tempo / high end / intense runs. In theory, once you have the proper base, you should have the ability to take easy days completely off during the season without any negative effects.