Is it obligatory for a woman whose fetus died after she refused to undergo a procedure to save it, to offer expiation or fast, knowing that she chose to complete the pregnancy based on hope for healing and fear of the fetus being disabled, and out of a sense of guilt?

What the questioner mentioned does not make her liable for a جناية (felony) against her fetus or for causing its death. The doctors gave her a choice between two options, both of which had the potential for death and life. She chose one of them, and there is no negligence in that, especially since the other option also had the potential to lead to death.