Robert Lincoln Death Threat

[Gene C]

In Jason Emerson's "Giant in the Shadows", on page 150, in 1869, Robert Linclon is working on a legal case and is staying with an Eli Royce of Escanaba, MI. Eli had an invalid sister, whom he had hired a nurse to help take care of her.

"When the nurse was asked to wait upon table at diner and told that they had Mr. Lincoln as guest, The young lady flew into a passion and said she would wait upon the table with a pistol in her hand. She was a niece of Wilkes Booth, who assassinated your father. It is almost unnecessary to say that she was immediately dismissed."

No names were mentioned, and the footnote only refers to a letter Robert had written. My question for all you Booth historians, who was this lady and which of John's brothers or sisters were her parents? (I have no idea)