Harper Lee's family line, particularly her mother's line was filled with character names. Her mother's name was Frances Cunningham Finch. So her mother's maiden name was Finch, and it appears her mother's mother's maiden name was Cunningham. The first name Frances was also used but for the name of a boy and it was spelled Francis in the book.

It would be interesting to ask her about her choices because everything seemed to have such rich meaning in her book. So, in short, the answer is her mother. But spending any time thinking about the ironies of that might lead you to draw some really strong connections and conclusions.