Please have your vet check her for an abdominal hernia. It is a gap in the abdominal wall that can allow a loop of bowel to push through. If this happens that loop can become "strangled" which can be very bad.
I am not saying that is what she has....it could be simple edema......but have it checked out.
It isn't something that you have to jump right on. I wouldn't put much work on the horse until she is cleared. It isn't that uncommon in horses. . It can often be surgically repaired as well.
Here is a link to photos of equine hernias