Not sure how sati could operate as a form of colonial resistance. Although sati was banned by the British in 1829, when in 1834 the maharaja of Rajasthan, Man Singh, died his 15 wives left their hand prints at the inner gate to the Mehrangarh Fort before they laid themselves on his funeral pyre. Many would have been children, unfairly widowed at 10 years old, facing either sati or a solitary life dressed in white, dependent on charity, working as menials.
Roop Kanwar committed sati in 1987, a voluntary act that pointed out a serious clash of values between urban India and traditional village practice and lead to a trail where eleven people were charged with glorification of sati.
It seems all of a part with purdah, the burkha, child marriage, honour killings– things incomprehensible to me, child of the late 20th century west that I am. Feminist theory claims that empowerment comes from 'owning' such things, finding power in being scorned and reviled, viz the current furore around the slut walk. In theory perhaps, but in practice, one needs to live several centuries to see the benefits.