The manager doesn't mention that prices can change over time, but this doesn’t describe a flaw in her argument. Her argument addresses the price of her factory’s automobile parts compared to the price of other factories’ parts. Whether prices change over time is irrelevant.

The manager shifts from treating refurbishing the factory as one way of making products more competitively priced to treating it as the only way. In her premises “refurbishing” is a sufficient solution, while in her conclusion it’s a necessary solution.

The manager doesn’t make this mistake. Instead, she argues that one thing is necessary for another when her evidence indicates that it is in fact only sufficient.

The manager’s argument is actually flawed because it recommends— and even requires— a solution to a problem without first considering other possible solutions to that problem.

The manager does make a definite recommendation: refurbishing the factory. She also establishes that refurbishing the factory would be effective at making products more competitively priced.