There's a death in India on 16th March 1870: Mrs M E Dukes, age 27, wife of W J Dukes of the E I Railway. Buried same day at Fort William. Might that be her? She died of pneumonia.
EDIT Perhaps not - this is probably a Mary Ellen Benns who as Mary Ellen Holmes, a widowed minor, married William Joseph Dukes in Fort William in 1860.