Are her ankles swelling too? Pregnant women's circulation suffers too, I've seen, late in pregnancy, and fluids will just drain to the lowest spot.
No, she doesnt have any other swelling at all. Just under her belly. The vet said she was in good shape. Vital signs good. He didnt appear to concerned at all and said the swellin should go down after she has foaled. He also said she was mushy by her tail, but although bagged up some, she still had some to go.