I think ultimately it's your fault. You installed lights that draw too heavily and caused her breaker to trip. You knew that the breakers trip every year, so you should have suspected a tripped breaker. Therefore, you were the proximate cause of the "incident." I understand that the information you were given wasn't the greatest, but it seems like it was your fault to me.
Ask yourself, would her breaker have tripped and caused her food to spoil if you had not installed the lights? If the answer is no, then it was your work that caused the breaker to trip (even if it was from a vacuum), so it's your fault.