Rebecca's father, Isaac Pennock, was the first member of the family to begin working with iron. The Pennocks were a well-established Quaker family with sizable tracts of land obtained under grants from William Penn. Primitive Hall, a restored landmark of colonial life located in West Grove, PA, was the ancestral seat of the Pennock family. 

Great Britain's repression of America's iron industry had resulted in a scarcity of iron mills and products in the United States. The growth of industry, caused by the first Industrial Revolution, led to an increase in the demand for iron products. Isaac saw this demand as an opportunity to get involved with the iron industry. In 1793, despite family reservations about leaving the security of farming for the uncertainty of an iron business, Isaac established the Federal Slitting Mill along Buck Run, about four miles south of Coatesville.

At the Federal Slitting Mill, cast iron bars were purchased from local forges, brought to the mill by wagon, heated in a charcoal-fueled forge, then rolled or hammered into rough sheets. The sheets were then cut or “slit” into strips which could be fashioned into wagon wheel rims, barrel hoops, nails, and other useful products.