No, you did not do the wrong thing. Remember, SHE created this situation. It is your job to supervise, and as such I am guessing that you have at least a tad bit of responsibility to report certain things to your manager regarding the running of the facility. If you kept this information to yourself and didn't tell your manager, could you possibly be putting your own employment status at risk? I'd say that's a very good possibility! I don't agree in being a snitch, but this is a matter that pertains to the running of the facility and it is not fair that she try to screw the facility out of money. Some may say this is stealing, and as such, can be a reason for being fired. She is essentially stealing from the business. Try to reframe your thinking like this, and you'll be assured that you did in fact do the right thing.