I remember reading something about them developing gas. :) One of the signs that I read about was the mucus plug being released, which is supposed to happen between 24-48 hours before foaling. I am not really sure what this is supposed to look like though :)?? That is so nice that your vet is close...if all else fails, you can just call when her water breaks. :)
When you have time and energy after the foaling, I would love a description of what sort of things happened around the actual foaling. It was helpful for me to just read about the signs you are seeing now :).