Ceiling fans are so inexpensive now. Are you sure you want to salvage it?
Assuming it is a very expesive fan, and that you don't want to suspend the "guilty child" from a blade that would counter balance the problem...I would consider measuring the distance from the ceiling to each blades high and low points, to determine how much of an adjustment needs to be made. If you can't realign it or if it cracks, I understand you must replace all the blades (maybe even the arms). That's why I asked if you want to salvage it.
I am NOT a repair or sales person but you can find numerous idea (generically presented) at