Using office resources for private business

Eva was a clever and efficient staff member working on a fixed-term contract in a large firm.  She could easily complete her assignments before the deadlines; but she preferred not letting other colleagues know about that because she did not want extra workload given to her and making other colleagues look less capable.  Being a fixed-term contract staff member, she understood that she would leave the firm at the end of the contract.  Hoping to make her mark one day and to secure future income, she was thinking the possibility of developing her side-business during the office hours by using the firm’s resources while pretending working on certain projects in the office. 

Eva thought to herself: it was not her fault that she was more efficient and capable than other colleagues.  She was only a fixed-term contract staff member and would leave the firm one day.  She needed to prepare herself for the future.

Was that justified for Eva’s secret plan?  What about the interest of the firm?  What factors does Eva need to consider before taking her course of action?