The River of Doom takes something that could be very dull and tedious (reminding your student to lift her wrists) and makes it entertaining and memorable.
Tell your student that there is a river running underneath the keys. Place your hand, arm or a ruler at this level and tell her this is the River of Doom. If her wrist falls in, she will have to swim to shore and restart the piece.
The aim of the game is to end the piece without falling in the River of Doom at all.
Assign practice with an imaginary River of Doom and repeat the game at each lesson until the Wrist Drowsiness goes away.
Wrist Drowsiness: Bounce
Your student’s wrists should be supporting her hands when she’s at the piano, with a level of buoyancy, but not laziness. This rubber band exercise will give her a feel for what that’s like.
Place a large rubber band or hair elastic around your student’s wrist and hold up one end so that the elastic is a little taut.
Ask her to push down with her wrist and, while she is doing this, pull up your end gently so that she can only drop it a little before bouncing back up.
Allow her to experiment with the different ways she can move her wrist within this setup.
Ask her to place her hand on the keys and then repeat the process.
Then ask her to play her piece (one hand alone or hands together) with the rubber band still around her wrist. Pull up a little if her wrists start to droop down.
Finally, remove the rubber bands but tell her to imagine they are still there and play again.
Give her the rubber band to take home and tell her to experiment with them in the same way, one wrist at a time, before starting her practice each day.