Naaien means to sew. A naaister is a seamstress.
In the past, professional naaisters were typically poor women, though women of all classes were taught the basics. Naaien could be done from home, and was an employment possible for women with young children. It is one of the few occupations open to women with children out of wedlock, who would rarely be welcome to work as servants in “respectable” households or stores.