Grant Fisher ran a 4 min mile in HS with no speedwork:
"Scannell somewhat infamously told Jeff Hollobaugh for the Mercury-Times that his athlete did no speed work in preparation for his 4:02 win at the adidas Dream Mile last year, or either of his Foot Locker championships.
The difference between mile-paced intervals and pure "speed work" is about five to 10 percent - or, the difference between "comfortably hard" and going to the well."
The 800 and 1600 are still primarily aerobic events. Look at Symmonds training. Lots of 1k repeats, tempo runs and mileage. The speed work was just the icing on the cake.
If she kept her aerobic fitness up with cross-training while being injured, perfect. Talent (and speed is highly genetic) doesn't go away with some weeks off, and she was able to show hers in the race!