int fadeAmount = 5; this could be 'byte' if the sketch keeps fadeAmount 0-255
unsigned char encoder_A1_prev=0; these could also be 'byte'
Looks like your daughter is going to be a programmer.
Edit
Not sure you saw this:
Maybe have a potentiometer the can be adjusted to create a 'divisor'.
It would be used to divide into all three: R, G and B values to set brightness/intensity.