Esther Kiobel is testifying in court in The Hague, demanding compensation from the Netherlands-based firm.
She is among four women who accuse Shell of being complicit in the hanging of their husbands by Nigeria’s military in 1995. Shell denies the allegation.
The activists led mass protests against oil pollution in Nigeria’s Ogoniland.
The protests were seen as a major threat to then-military ruler Gen Sani Abacha, and Shell. They were led by author Ken Saro-Wiwa, who was among nine activists hanged by the military regime.
Their executions caused global outrage, and led to Nigeria’s suspension from the Commonwealth for more than three years.
Two of the widows were in court, but two others were denied visas to attend.