If she was pastured bred, it could be the last month she was left with the stallion.
Ok, let me think, I do beleive its 21 days.
There are so many "animal cycles" I keep up with.
If not correct, some one correct me on this.
She can bag up for weeks before foaling. You can calculate to dooms day and will still be off because you dont know exactly when she was bred.
Its now waiting and before you know it, the foal will be here and allready up sucking.
Much luck to you and a healthy foal.