Colonial seamstresses typically worked either as milliners, who sewed shirts and what would today be considered accessories, or as mantua makers. Mantua makers were gown makers.
The term "seamstress" really wasn't applicable in colonial times, as the tailoring profession was dominated by men. Although some women achieved the role of mantua maker, apprenticeships in the area were rare and required seven years of commitment to learning the trade. To a degree, milliners also played the role of fashion advisors, as they were sure to keep their clientele advised of the latest and most up-to-date fashions from the European continent. According to Colonial Williamsburg, while specialization was the trend in the European tailor and milliner industry in colonial times, colonists were much more general in their skills and knowledge.