A: Upon the death of the husband, the wife goes immediately into iddat. And a woman in iddat is not allowed to perform Hajj but if she did do the Hajj, it will be valid.
If this lady was able to go back to her hotel in Makka then she should have done that. If not, then she should proceed with the rest of the Hujjaj to Arafaat and thus complete her Hajj. Sometimes, due to local traffic control regulations, she might not be able to go back to Makka immediately. She will therefore, continue with her Hajj. Once done, she remains in her hotel room until it is time for her flight back home. Upon reaching home she will resume her iddat in the house where she lived.
Allah Knows best.
Mufti Siraj Desai