I don't understand your vet's hesitation to palpate her because she hadn't been palpated before? If she had been ultrasounded, she's been palpated. I DO understand the need for sedatives and the hesitation to do it on that count. LOL. I have a lot of tricky, touchy mares who don't like the whole ultrasounding process either.
A month and a week is a long time for a foal to grow. I recently had a maiden mare foal who didn't look pregnant. But she did look bigger than your mare does in the pic. (Beautiful mare, btw! I'm an Arab person...what is her bloodline? Is that Thee Desperado in your avatar?)
Personally, my guess would be that she is not pregnant. I would have a vet out to check her though. If she really isn't pregnant, at least you'll know and you don't want to miss this breeding season to get her pregnant again.
A good horse is worth more than riches. ~ Spanish Proverb