Will the daughter be sinful if she disobeys her father in his choice of a difficult medical specialization that she does not desire, knowing that it will cause her great hardship, and is the father entitled to compel her to pursue this specialization?

You are permitted to disobey your father regarding his insistence that you pursue a specialization you do not desire. You are not obligated to obey him in this matter, especially if it leads to negligence in the rights of your husband, your home, and yourself. Obedience to the husband takes precedence over obedience to parents.