I hate to tell you this, but you're going to have to watch and see. She's doing it like my mare and keeping it hidden well. Izzy is at day 349 and doesn't as of last night have any more udder and just a tiny bit of a belly, nothing like the other pregnant mares you'll see here. I would suggest you try the pool test strips and she might give you something. Keep watching her udder closely. She's started to get some fill, hopefully it will turn into a real udder and let you know or possibly she'll have a real baby belly closer to foaling. You might be in for a lot of long nights waiting trying to guess. Welcome to foal watch!!