The superior vena cava (SVC) is the main vein that drains the head and neck blood vessels and returns blood to the heart on the right side. There typically is a vein that extends from the left shoulder to the SVC called the innominate vein, which collects the blood from the left side of the neck and the left arm. Rarely, there is a left sided SVC, as well; there can also be a bridging vein between the right and left SVCs. This is a normal variant. However, without evaluating your daughter, I cannot say if what they are seeing is normal or not, and what the structures are, so I cannot tell if they need intervention and what complications there are. A pediatric cardiologist who specializes in fetal cardiology would be helpful in defining the anatomy and letting you know if the vessel that is seen is normal, or not, and the associated consequences.
Thank you for your answer!. Ill be posting the diagnosis tomorrow whenever we find out.