"Hot potato" drills might work; think a remington or chromatic exercise that flicks between a stable long tone, and a very short target note. Ex: Whole note G-----(sixteenth or shorter F#) whole note G. Middle note changes chromatically, aiming for speed and accuracy. This can evolve to metered trilling, swapping between two notes in eight notes, tripalets, sixteenths, and so on.
The tendency with technique is to focus on the downward motion of the finger, when the upward motion is absolutely equally important, and more difficult to train. How far do the fingers come off the keys? Do they fly into the air, expending extra energy to flex the fingers away from the instrument, or do they simply release tension? Think about pulling a cork out of a wine bottle; all the tension is gone the second the cork releases. In the instant of lifting a finger, a good amount of force should be applied over a VERY short distance, creating a fast action that doesn't travel far. If the fingers are closer to the instrument, accuracy increases, and the available applicable force decreases. You can't hit as hard from a shorter distance.
Have her hold out a C below the staff. Can you lift her fingers off the keys easily? Same for C in the staff. Do her fingers release tension without a fight?
Hope this helps!