May a working widow go out to work during the ʿiddah of death?

Yes, if there is a need. Scholars of the Shafi'i school permit a widow to go out during the day for needs such as working to earn a living, buying necessities, going to hospital or administering the estate, since there is no longer a husband to support her. However, she should return and spend the night at her home. When she goes out, she still observes ihdad: no perfume and no adornment. Unnecessary journeys such as holidays, celebrations or a voluntary umrah should be postponed until the ʿiddah ends. Employers in Malaysia usually give compassionate leave; some government agencies have special ʿiddah leave, so check your employer's policy.