That definitely was a huge part of the problem. Instead of being pushed by Salazar towards extreme caloric restriction and unhealthy weight loss, Mary Cain should have been doing a body recomposition, partaking in frequent resistance training alongside running and cross training. This in would allow her to naturally get leaner, despite little change in weight. Not would this have improved her running performance but also significantly improved her resistance to injury. Eating enough to allow for energy balance along with doing regular strength training would enhance bone mass and density, which very likely would have prevented the stress fractures she experienced.
The reason why Mary Cain developed five stress fractures is from not having enough energy to support both health and performance. When you are an aggressive caloric deficit, the body's ability to recover and absorb the training stimulus is compromised. Not surprisingly this makes injuries much more likely, lacking sufficient calories/nutrients to promote tissue repair. Additionally, being in substantial negative energy balance can trigger ammenohea being as another major contributing to the stress fractures Mary Cain experienced.