Stowe provides further details about her story based on actual events in A Key to Uncle Tom’s Cabin.
The character of Mrs. Shelby was based on the sentiments a Southern women expressed to Stowe on a trip to Kentucky. A friend of Stowe’s was born and educated as a slaveholder. In a conversation with Stowe she said, “I never thought it was right to hold slaves. I always thought it was wrong when I was a girl, and I thought so still more when I came to join the church.”
These words were adapted to fit the story and were spoken by Mrs. Shelby.
The full story of this connection can be read in Part 1, Chapter III “Mr. and Mrs. Shelby” of A Key to Uncle Tom’s Cabin.