In this particular incident, again, it was the position of the department that this wasn't necessarily wrongdoing. This was more of an error on her part, and she really shouldn't have signed it. She was acting on behalf of her manager. The invoice came in, and I think she should have waited and had that invoice signed off when her supervisor returned.
Unfortunately, I can't speak for the employee. I'm assuming she wanted the vendor to be paid promptly within the terms of the contract.