Green was a successful businesswoman who dealt mainly in real estate, invested in railroads and mines, and lent money while acquiring numerous mortgages. The City of New York came to Green for loans to keep the city afloat on several occasions, most particularly during the Panic of 1907; she wrote a check for $1.1 million and took her payment in short-term revenue bonds. Keenly detail-oriented, she would travel thousands of miles alone—in an era when few women would dare travel unescorted—to collect a debt of a few hundred dollars.