But the child was so proud of her pretty shoes that she never took them off except at night and when she took her bath.

The Witch was too much afraid of the dark to dare go in Dorothy's room at night to take the shoes, and her dread of water was greater than her fear of the dark, so she never came near when Dorothy was bathing.

Indeed, the old Witch never touched water, nor ever let water touch her in any way.
But the wicked creature was very cunning, and she finally thought of a trick that would give her what she wanted.

She placed a bar of iron in the middle of the kitchen floor, and then by her magic arts made the iron invisible to human eyes.

So that when Dorothy walked across the floor she stumbled over the bar, not being able to see it, and fell at full length.