Who is the second Mrs. Bruce from Incidents in the Life of a Slave Girl?

Mr. Bruce's second wife is a wealthy, American aristocrat. Completely opposed to slavery, Mrs. Bruce speaks out against it, and eventually buys Linda from the Flints to insure her freedom. Mrs. Bruce is a courageous woman, who doesn't merely disapprove of slavery, she vebalizes her disapproval and acts on it as well.