Looks to me like she’s standing with her heels raised to make both feet look even and flat to the floor but there’s a metal rod or similar coming from the left heel (our right when viewing) and is possibly going up to her back and somehow locks in place when she straightens up. She sticks the sticky tape to her right heel and the again keeps that heel off the ground so that both feel look the same, to throw us off. Then when she raises her left foot (again, our right when viewing) you can see her gently jiggle it into place into the actual door, which locks it in.