Mileage Reimbursement

So my wife just informed me that our school district that she is teaching for is trying to make her drive 1.5 hours to go shadow another teacher for Professional Development. The school is making every teacher in the district do this. They are telling everyone that they will not be reimbursed for the mileage. Is this legal? With the prices of tires, fuel, and getting an oil change, this seems a bit ridiculous to me. I have tried looking it up and can’t find anything on it. We are located in Missouri. Any help is greatly appreciated!