Her behavior has been reinforced (i.e. strengthened). Reinforcement can be external or internal and can be positive or negative. If a child wants approval from parents or peers, this approval is an external reinforcement, but feeling happy about being approved of is an internal reinforcement.
It remained to define the unit of amount of substance by fixing the corresponding mass of carbon 12; by international agreement, this mass has been fixed at 0.012 kg, and the unit of the quantity amount of substance was given the name mole (symbol mol).
Like all units, a mole has to be based on something reproducible. A mole is the quantity of anything that has the same number of particles found in 12.000 grams of carbon-12. That number of particles is Avogadro's Number, which is roughly 6.02x10 23. A mole of carbon atoms is 6.02x10 23 carbon atoms. A mole of chemistry teachers is 6.02x10 23 chemistry teachers. It's a lot easier to write the word 'mole' than to write '6.02x10 23 ' anytime you want to refer to a large number of things! Basically, that's why this particular unit was invented.