She’s a bean counter and has a heater.
She's a biotch....
That’s part of her mentality but there’s more behind this.
I would bet the business is not doing well and she is taking the stress out on the employee’s small screwup. And/or something has gone on there where she feels the employees don’t respect her enough and she’s being a hard ass to possibly get the ones she doesn’t like to get in line or quit. Her reaction is emotional to punish, not logical or financial, as getting a cheap programmable thermostat would solve the problem. A person who just wants to make sure the heat isn’t left on would just get a programmable thermostat and take the issue out of everyone’s hands, no more problem. She is ‘teaching them a lesson.’
There is more to it.