Sara Herwegh was the maternal ancestor of the well-known Sahlgren family in Gothenburg. As a widow, she ran an extensive trading company in Gothenburg at the beginning of the 1700s.

Sara Herwegh was born in Gothenburg in 1651. Her father is assumed to have been Jakob Herwegh Junior — certain sources state instead that it was his brother Adam Herwegh who was her father. Her paternal grandfather, Jakob Herwegh Senior, was one of the first Gothenburgers, having immigrated to Sweden in 1610—1620. His origins are the object of controversy, but the name Herwegh points to roots in the Netherlands or perhaps Germany. Jakob Herwegh was in charge of the scales for weighing iron while both his sons, Adam Herwegh and Jakob Herwegh Junior were active as merchants in Gothenburg. Jakob Herwegh Junior was also appointed to several important positions of trust in the town.

Sara Herwegh entered into her first marriage with Cornelius Pietersson van Egmont in Gullberg and she was therefore known to some as Sara Gullberg. Her husband was a deacon in the German-Dutch congregation. The couple had three children. However, Cornelius Pietersson van Egmont died in 1679. Sara Herwegh remarried, this time to Nils Persson Sahlgren, a merchant and councillor in Gothenburg. It is unknown how many children she bore in her second marriage, but at least four are known: her daughter Anna Maria and her sons Jacob, Niclas and Peter.

Sara Herwegh took care that her children should have a good education, at least her sons in her second marriage. Her son Jacob Sahlgren was sent to study at Uppsala University in 1700. Her son Niclas Sahlgren, born in 1701, was sent at the age of 16 to Holland for business education in Amsterdam. Even Peter Sahlgren travelled abroad when young, to Italy for his education, but died early, in 1722. Her daughter Anna Maria Sahlgren married Hans Olofsson Ström, a wholesaler and works owner, in 1713.

Nils Persson Sahlgren ran a trading company in Gothenburg and when he died in 1703, Sara Herwegh took over the business. Their son Jacob Sahlgren was called home from his studies in Uppsala when his father died, to assist his mother in their business. He remained in his mother’s service for somewhat longer than a decade, and only in 1716 was he made a burgher in his own right. The trading carried out by Sara Herwegh under her own name was, like her deceased husband’s, both comprehensive and successful. The trading company exported iron and masts while imports were mainly salt and cereals. Apart from export and import trading, she spent much of her time and energy on considerable credit-giving enterprises for the majority of the central Swedish iron works. During the early 1700s, Sara Herwegh was the fourth largest iron exporter in Gothenburg and in the taxation records from 1715, she is listed as the town’s wealthiest citizen.

When Sara Herwegh died in 1727, she left a considerable inheritance. Both her sons, Jacob and Niclas Sahlgren must have drawn great advantage from their inheritances since soon after their mother’s death they started comprehensive investments in industry and trade. Jacob Sahlgren started the first – and for a long time only – sugar refinery in Gothenburg in 1729, which was later run by his widow Brigitta Sahlgren. Together with, among others, their enterprising friend Jonas Alströmer, both sons were also engaged in two great trade projects, one directed at the West Indies and the other at the East Indies. Their inheritance from their mother must have contributed significant capital in both cases. The West Indian project was never a success, but the East Indian project was a success, to put it mildly. Niclas Sahlgren in particular is counted among the group of initiative-takers to the Swedish East India Company at the beginning of the 1730s. Both Jacob and Niclas Sahlgren were prominent businessmen and became enormously wealthy. Niclas Sahlgren allowed part of his wealth to be donated as the linchpin in a project to create a "salutary institution" for the general public, that in due course took form through the founding of the Sahlgrenska hospital, nowadays the Sahlgrenska University Hospital in Gothenburg.