Can you get a vet to check her again? That way you'll be sure it isn't a false pregnancy. My gal Abbie was looking pregnant but not ready at 343 days from last breeding and so I had the vet check her then... there was a live foal, so I put her in a camera stall and put a foaling pager on her. Well, now she's 371 days along and still not looking as "ready" as most other mares look! But we know for sure there's one in there, no way could it have gone missing after 343!