A student writes:
I've started some new finger strengthening/independence exercises and my left pinky is giving me some trouble. In one exercise, I have all five fingers of left hand pressed down onto keyboard bed (proper wrist position, etc) and I hold 4 fingers down while taking the 5th finger and playing the key a certain number of times (16-20) with one finger- up and down, etc.
I think she has a misunderstanding about how the fingers work. They don't want to play by lifting away from the hand; they want to play by rotating into the key with the forearm behind them. The 5th finger (and the 4th) are much maligned when called weak. There is nothing wrong with them. We pianists don't train for strength the way athletes do; we train for coordination of refined muscles. It takes very little physical strength to play the piano. She is definitely on the wrong track when holding down other fingers and lifting her 5th away. (Dohnany wrote some exercises along this line, which I think are destructive.) 
The fingers gain strength by having the forearm behind them. This is achieved with the 5th by slightly rotating the forearm toward it. The motion is rotary, like turing a doorknob. But this is very difficult to describe in words and has to be demonstrated, which I do an earlier post. I hope she doesn't hurt herself.