You are right that the table is not flush with the window wall, but I think you have the table edge wrong. It is a straight edge from corner to corner. What is interesting, is that she has pushed aside the blue-green table cloth so that it will not be soiled by bread crumbs or spilt milk. Maybe she has moved the table away from the wall so that she has extra space to do the pouring. (Or maybe Vermeer just wanted her to be more in the light!)

For me the central feature of the painting is the extreme care she is showing in pouring the milk slowly and in a specific place. She has to tilt her head to get a proper view for carrying out this delicate task.