The woman, who has not been named, lit the device which she set up in the family kitchen before leaving the house.
Her three-year-old granddaughter collapsed when she was overcome by the deadly gas later that afternoon and was treated in hospital with five of her relatives.
They included two boys aged two and 10 months, a four-year-old girl and the woman's two daughters-in-law, aged 26 and 29.
Firefighters were called to the home on Hockley Avenue, in East Ham, east London, on Wednesday afternoon, soon after the grandmother set up her make-shift launderette.
