Who is Tanoo from Swimming Lessons and what is their importance?

In "Auspicious Occasion," Tanoo is for two years Rustomji and Mehroo's gunga (house servant), too old and feeble to keep from accidentally breaking things and doing an inferior job cleaning. Abandoned by her husband, she raises two sons who become drunkards. Mehroo feels sorry for her, but Rustomji is hardhearted. Tanoo's decrepitude and clumsiness demand that hard-hearted Rustomji fire her, but they arrange for her to return to her native village.