Think of her roots as being her feet, you have had her feet wet for 3 days now with no sign of them drying out. Eventually she will start developing root rot since her feet are staying wet for such a long period of time and not being allowed to dry out. Flushing on the other hand gets her feet wet but since you are doing it all in one shot, all that water is going over her feet in a short period of time, working more like a wash of the roots, and since the soil can only hold so much water, after you are done, her feet are no more wet then what they should be when you normally water her. But you have to allow her feet to dry out before you get them wet again. Allow air to get to them.
Think of your own feet. Sure they are wet every day from taking a shower but then you dry them. If they were wet all the time and not allowed to dry imagine what your feet would look like after 3 days, or even a full week.