Thank you for the quick update! This diagnose (innate/genetics) should be quite a relief, as it showed there is no deadly virus circulating in your flock.
Unless the incubator had a disfunction, usually there is something wrong with chicks in need of assistance for hatching. Only your good care...
She might have suffered from an innate heart condition. These issues become more noticeable the older and bigger the bird gets, and adding the extreme cold and being chased might have pushed her over the edge.
I am sorry for your loss.