Profession of "Mantle Maker" had nothing to do with be a seamstress.
A mantle maker machined mantles for gas lamps. The mantle was made of impregnated metal nitrates and Thorium dioxide a highly toxic and radioactive substance.
Without the use of breathing apparatus protection while working in this environment you would be exposed to the toxic particles.
Phthisis, or lung disease was one of the more common causes of death when Mary Ann died.
Occupations, such as hers, were most likely contributory. "Stone Cutters",(masonry workers), died from this disease from the inhalation of dust.