Yes, she could be fired for this: even if at the end of the day, no harm was done (e.g. your wife paid everything), if she personally or employees generally did not have permission to use company cards for personal expenses, she misappropriated company resources. This is no different from taking your neighbor's car without permission for an urgent errand--even if you top off the case tank and take it through the car wash so it's in as good or better shape when you returned it, you still violated the law by using another's property withhout permission.If you wife does not have an employment contract, she is an employee at will and could be fired at any time, for any reason. But even if she did have an employment contract, using a company card for personal expenses would most likely constitute lawful grounds for termination.