Sara has been described as an "Indian trader", and served as a translator for the Dutch on a number of occasions as she was 'proficient' in the 'Indian Languages'. She established what would today be called a professional friendship with Chief Oratam, as they often worked together to craft language for agreements that would be understood by both the Native Americans and the Dutch.
Her house with Dr. Hans Kierstede was on the north corner of Pearl and Whitehall Streets, it is represented in the Castello Plan and appears to have a 'surgery' at the back, and a medicinal herb garden within their plot.
In 1661, the Burgomasters decided to erect an Indian Trading house in front of her house where the weekly market with Native Americans took place. (F1 on the Castello Plan, which does not show this because it dates to 1660.) Local carpenter Adolph Pietersen was eventually asked to build the small house in 1662. https://encyclopedia.nahc-mapping.org/document/meetingadministrative-meeting-burgomasters-100 The documents describe a significant pile of lumber at that location that was probably used to build the 'Indian Trading House'. This location was both close to Sara's house and close to the dock.
Indigenous people came to trade corn (maize), venison, firewood, furs, and probably spoke with her every week. So her language skills, and her ability to establish trusting trade relationships with the 'Indians' would have continued to improve over the years.
Sara kept Africans and Native Americans as slaves, and her last will , dated July 29, 1693 includes instructions to bequeath six enslaved people including:
"a negro boy, Hans to her daughter Blandina",
"my Indian boy named Aide [Andries] to her son Lucas
"a negress, named Susannah" to her daughter Catherine
"my negro Sarah" to her son-in-law Johannes Kip
"a little negro, called Maria" to her son Jochem
"a negro boy Peter" to her daughter Anna van Borsum
- "In the name of God, Amen. Be it known to all whom it may concern that I, Sara Roeloffse, late widow of Elbert Elbertse Stouthoff, considering the frailty and shortness of Human life, Do make my last will in manner following. 1st. I commit my immortal Soul into the merciful hands of God Almighty, and my body to a decent burial. 2Nd, I revoke all other wills. Now I will before anything else to my daughter Blandina, of this city, a negro boy, Hans. To my son Luycas Kierstede, my Indian boy named Aide. To my daughter Catharine Kierstede, a negress, named Susannah To my son-in-law, Johannes Kip, husband of my said daughter Catherine, my negro, Sarah, in consideration of great trouble in settling the accounts of my later husband, Cornelius Van Brosum, in Esopus and Elsewhere. To my son Jochem Kierstede, a little negro, called Maria, during his life, and then to Sarah, the eldest daughter of my son Roeloff Kierstede by Ytie Kierstede To my son Johannes Kiersted, a negro boy Peter I leave to my daughter Anna Van Borsum, by my former husband Cornelius Van Borsum, on a account of her simplicity, my small house and kitchen, and lot situate in this city between the land of Jacob Mauritz and my back house, with this express condition, that she shall not be permitted to dispose of the same by will or otherwise, but to be hers for life and then to the heirs mentioned in this will. It is my will that my son Luycase Kierstede shall have the privilege of buying the house where he now lives and the bake house and lot belonging to the same and to pay the money for the same to the other heirs, he to retain his share. I have fully satisfied my sons Hans Kierstede and Roeloff Kierstede for their share in their father's estate, being 40 Beavers, as by account for the same, the rest of my estate I leave 3 to the seven children of my deceased husband, Hans Kierstede, viz, Roeloff, Blandina, Jochem, Luycas, Catrine, Jacobus, Rachel, and the children of my deceased son Hans Kiersted by his wife Jannike equally. Only Hans Kierstede the eldest son of my deceased son Hans Kierstede shall have L1 for his birthright. I appoint as guardians of my daughter Anna Van Borsum, and managers of her house and lot my son-in-law Johannes Kip, and my son Luycas Kierstede, and my son-in-law Wm Teller, giving them full power as executors." NY Wills, Vol 0005-0006, 1693-1707 
Sara was born in Amsterdam, and travelled to New Netherland in 1630 with her parents to initially settle in Renssalearswyck near present day Albany. Her first marriage was in 1642 to Hans Kierstede, the DWIC company surgeon. She was 15 years old. She and Hans had many children, so managing their household was no small feat. She and Hans also had a medicinal herb garden at their house.
Sara was the eldest step-daughter of Domine Eduardus Bogardus, as her mother, Anneke Jans, had married him following her widowhood. So she, and the women in her family, were very aware of the governance of the settlement, and the goals of the Dutch West India Company. She must have been a respected member of the Dutch Reformed Church, because she was frequently called upon to witness the baptisms of more than 20 of her neighbors children.
Sara's second marriage was to Cornelis van Borsum in 1669. They had a single child who may have had learning disabilities.
In 1664 she acted as an interpreter in negotiating a treaty for Petrus Stuyvesant with the Indians of the Hudson River. For her services as interpreter, a patent was granted to her second husband on 14 Oct 1673, "of a lot on Manhattan Island, north of the windmill on the west side of the road that runs to Klatchook."
Her third marriage was to Elbert Stoothoff, in 1683, just 10 years before her death at 56 years of age.
In 1853 Kiersted's Universal Remedy, an ointment containing herbs was still being sold to women as a cure for maladies relating to breastfeeding. We don't know for sure, but it is possible that Sara and her husband Hans, and her grandmother the midwife may have contributed their knowledge of herbs and trading with the Native Americans in the making of this remedy.