She should not be standing all that much--and should not be sitting much either, not even on a doughnut. Using the doughnut does take direct pressure off the tear, but you still have the pressure of gravity bearing down upon the tear. Better to lay down, or only use a recliner for now. It sounds like a small tear, so it should not take too much time to heal if she can avoid sitting straight up, and also avoid being on her feet much for another few days at least. If she could lay around a lot, and put ice on her perineum for 20min at a time, 3-4 times a day, that will help reduce swelling and hasten healing. She should also rinse off her perineum with water, every time she uses the bathroom--use some kind of squeeze bottle and use it to rinse. At night, to get plenty of air to the tear, she can leave off her pad, and just sleep on a chux pad or towel.
It takes as long as it takes to heal--she can help that go faster by using ice, etc--but you can't push it or you will just make it take longer. She should avoid doing anything that makes it hurt more!