Auditors say that many such cases of ongoing, systematic fraud or embezzlement start with a small incident that may not even have criminal intent. For example, maybe she sent a personal UPS shipment or bought some gas for her personal vehicle on the company card and intended to reimburse SL. Then she forgot about it and realized they had, too. 

Next, small thefts (by now she probably realized she wouldn't repay them, although perhaps she rationalized that she still intended to) became a pattern, and as each one went undiscovered, she became more bold and also better able to rationalize them ("nobody seems to even notice!").  Once it is an established habit, the person steals freely up to the limits of their opportunity.

This, of course, is why it is necessary to have oversight in place to identify and address the small problems before they become big ones.