I've since found out a little more about Bristow's "mistress"....
It seems that Mahondy Khanum was HER name. In her will Mahondy names a brother Mirza Husinabe Beg and nephew Mirza Museetah.
She may have gone by the English name Hannah Bristow, for a Hannah Bristow, described as a native woman aged 74, was buried on 17 Sep 1834 at Dum Dum.
Mahondy and John Bristow's other daughter, Mary, married James Tillyer Blunt (c1765/6 - 1834) at Calcutta on 3rd September 1796. Blunt was a Captain in the Bengal Engineers. They had a son and three daughters. In 1851 these daughters were "landed proprietors" living at Wonford House, Heavitree, Devon. The son, Richard Tillyer Blunt, married Caroline Lavinia Bridget Sabine, widow of Robert Richard Percival Brereton, and he died in Devon in 1875.
Mary Bristow and her sister Charlotte were shipwrecked on the coast of Madagascar in 1792 whilst aboard the East Indiaman "the Winterton" en route from England to India. Clearly both survived and went on to marry. Living for months in the wilds of Madagascar and captured by the French, their adventures are noted in the book "Marked for Misfortune".