What Causes Swelling Of Feet In Infants During Birth?

My daughter was born prematurely at 32 weeks gestation and both feet were swollen. Her father has other children that were born with both feet swollen as well. These children were born full term. Their swelling on both feet went down by the time they reached a year. My daughter is 8 months and a few weeks old and her right foot went to normal by the time she was 3 months old while the other is still swollen. She is not walking yet and one of her feet are still swollen. We had her be tested for Turner s Syndrome and it came out negative. She was also tested for heart condition and poor circulation and it also came out negative. I am worried now that her other foot is still swollen. Why has this not gone down yet? Is this hereditary? Or a condition not yet found by her pediatrician?