In the case of a disease, there's really nothing she can do, and iirc the film implies the hard choice here was to decide to have a child even knowing that will die.
In the car of an accident, there is the feeling that she could literally have prevented her daughter's death by preventing the accident, but "chooses" not to. The free will implications of that are much more interesting imo.
(To be clear, it's one of my favorite stories and also one of my favorite movies.)