Hi Sara, I (fortunately!) have never dealt with shin stress fractures, but the last long run for my first marathon sounds pretty similar to yours! I found that incorporating yoga into my cross training during my last marathon made a world of difference! Some studios/ gyms even offer specific yoga for runners classes and there are some really great yoga for runners books out there where you can find stretches to target specific areas (hips, piriformis, calves, etc.) - for running some of my favorites are pigeon pose, squat, and triangle forward bend!