While ice skating, Tabitha pushes against the wall to stretch her leg. What is the reaction force?

The force exterted and / or experienced by Tabitha's leg is an opposite reaction force equal to the amount of force she exerts when she pushes against the wall. This is explained further on Newton's third law of motion. Otherwise should the force she exerts on the wall overcomes the force of strength of the wall's resistance, the wall will break to the direction of tabitha's push.