If you look at world records across a range of distances a decent rule of thumb (but by no means extremely accurate) is that women's times are around 10% slower than men's. Thus I would say 4:30 male is around 5:00 female. I'm assuming mature people here and there may need to be some adjustment for HS. Someone mentioned girls maturing sooner than boys so logically that should reduce the 10% fudge factor if it's appropriate.
Now if we're talking about "equivalent" in the sense that X would win the state meet for boys and Y would win the state meet for girls, that's something entirely different.