deseraewatters your mare can foal safely in a pasture . Unless, it is small and overcrowded with horses you need not put her in a stall.
All my mares foal outside and have for over 35 years.
Your mares teats look very full and that is a sure sign that they are about to foal. You may want to check on her every 2-4 hours for the next couple of days.
The whole process of foaling should take no more than an hour.
It might take the foal that long to stand,
I you can save the placenta and have the vet check it out to ensure that it is whole Mares have been foaling for 1,000 of years most do so without problems. I wouldn't worry too much. Enjoy the foal. Shalom