If your pasture grass is fescue, that could cause a problem as far as grazing during the later stages of pregnancy. Your county extension agent might be able to help you find out about fescue in your area, and/or where to take a sample of your grass to have it looked at.
Based on what you have said about her foals, her being a roaned blanket rather than a fewspot does seem likely-- that does not mean all or even most of her foals will roan though-- for example, my stallion above ^^ roaned, but most of his offspring have not. He sires mostly blankets that do not roan, with an occassional roan-- for example, these four adult geldings/stallions are all sired by him, out of Thoroughbred mares--
And the mare on the left has an Appaloosa dam-- the mare on the right has an AQHA dam.
So, depending on the mare, stallion, and serindipitous Appaloosa luck, your offspring colors/patterns may vary .