I had similar PR's my sophomore year in HS (I'm a guy btw)...ran 4:50 my junior year in HS.
Just stuck to what the coach gave me and was diligent in my workouts. Just be patient, you're a sophomore girl in HS with very good times (I think so anyways), I would expect the coach is doing a good job. You have many good years ahead if you keep on it.
I tried breaking 5 numerous times, coming up short each time (5:02-5:05). Then the next week I ran 4:50. I had several veteran runners tell me that's how it usually happens. When you break 5, you really break it.
I hate running in the heat, and when I broke 5 it was 100 degrees out and sunny. My coach pointed out one kid before the race and said that he would go under 5. So I ran on his shoulder the whole race with all I had and ran 4:50. That whole race, my mind was empty. Ignored the clock, listened to watch my coach was telling me, and stayed glued to that kid.
It will be hard for a HS girl to find another girl near 5 flat to race (at least where I'm from), so just keep doing what you're doing, believe in what you're doing, believe in your coach, and believe in yourself.
Also, you didn't mention if you do anything in the winter, but you should definitely keep your fitness up, so you still have something to work with come outdoor. Perhaps talk to your coach and get some kind of plan in place.
Hill workouts can help maintain (or even build) your base, improve turnover, and are short enough in the winter that they won't be too miserable. I ran D1 in college, and during our long winter break, every week my coach had us doing
6-8x0.5 mile hills comfortably hard w/ jog rest
16x100m hills FAST, jog rest
25 minutes at threshold pace
Not saying you should do that exactly that, as you're in HS, but it should give you an idea