My sister had gall bladder removed &has now developed severe gastroparesis. if b/c vagus nerve damage caused, can anything be done to reverse?

Yes: I can't imagine the vagus nerve being damage during gallbladder surgery. Gastroparesis can be caused and treated in many different ways. There are meds to try and also some patients can be a candidate for a gastric stimulator to be placed surgically. See your doctor.

Unrelated: Gallbladder surgery in no way would injure vagus nerves. There is no association with these two conditions. Gastroparesis is uncommon and can be related to diabetes. Some medications can help, see a gastroenterologist to be sure the diagnosis is correct.