What would you do in this situation? Apply ethical principles to explain the rationale for your decision making process

Nurses face many ethical issues on a daily basis. Consider the following scenario:
Your unit has team nursing. As luck would have it, you and your best friend, Jill, are paired as a team this shift. Jill is a new nurse so you feel this is a great opportunity to take her under your wing a bit and show her the ropes. It is a busy shift and you administered Mr. Smith his insulin dose based on the sliding scale before lunch. You chart your medication administration and continuing caring for your patients. An hour later, Jill comes to you terrified because she forgot to chart the insulin she gave Mr. Smith and realized that you also gave the medication. She rushed to take his blood sugar and it was 115. Mr. Smith felt fine and was eating a candy bar his family had snuck in for him. No harm done, in fact he probably needed the extra insulin to compensate for the candy bar he wasn’t supposed to have, Jill explained. Jill begs you not to report this since she is still on probation. She says that she has learned her lesson and since nothing bad happened, why does anyone need to know?
What would you do in this situation? Apply ethical principles to explain the rationale for your decision making process.