Seems as if your client has poor strength in the musculature in her forearms. Have you ever thought about strengthening those muscles?
Too, you can mimic the movement of a push-up by performing the same push-up movement in a semi-prone position with an elastic tubing.
Lastly you can perform standing isometric exercises by having her press her open hand against a fixed stability ball with her elbow joint at varying degrees so that she develops isometric strength at her wrist and elbow at different angles.
Hope this helps.
You can build strength in the muscles that flex the wrist by doing wrist curls with a small weight and gradually progress from thoses