Just went back and re read your thread. Seeing as your not sure of her history and weather she may have had a foal or not before, I would say that there is every chance she is pregnant. She may be carrying the foal higher up if she is a maiden.
Now I think its time you saw "The photo"
Hopefully Chanda will be on sometime soon and will post it for you. It really goes to show that a mare doesn't need to carry the wide load look to be pregnant
Her Mare is a prime example not to discard her pregnancy possibility , just yet
One other thing before I leave work for the day is as she draws closer to foaling there will be less room for the foal to move and less action.
Some mares don't bag up until they foal. Diane (Castle Rock) says to look more towards her vulva and how her stomach looks. If there is concern that she will foal with no milk you can get your vet to give her a shot. Just give him/her a heads up.
I'm going to say some positive changes. She appears to be elongating -- shape seems to be changing some, and her udder certainly looks different. So, I'm still feeling positive.