Which spelling of her name is correct?
There are various spellings of her name.
The artist herself adapted her name and its spelling to the country in which she was living at the time.
The accepted convention in the German-speaking sphere is Maria Anna Angelika Catharina Kauffmann, and in the English-speaking sphere, Angelica Kauffman.
On her baptismal certificate of 1741 her name is written Anna Maria Angelica Catharina Kauffman in Latin script. In 1759 she herself wrote Maria Anna Angelika Kauffmanin v[on] Chur and in 1761 Maria Anna Angelica Kauffmann.
She signed her letters Angelika Kauffmann or Angelica Kauffman, depending on addressee, and following her second marriage also Angelica Kauffman(n)-Zucchi. (siehe Ill. 10)
In the title of his ‘Memorandum of paintings’, her husband Antonio Zucchi [PDF-File] gives her name as: Memorie delle piture [sic] fatte d’Angelica Kauffman.
In 1810/11 her second biographer, Giovanni Gherardo de Rossi, wrote a Vita di Angelica Kauffmann and reported that she was baptized Maria Anna Angelica Caterina.
In the different copies of her will, her surname is spelled with a single F: Maria Anna Angelica (also Angelika) Kaufmann.
In the inscription on the tomb she shares with her husband A. Zucchi in the church of S. Andrea delle Fratte in Rome, we can read both ANGELICA KAUFFMAN and, further down, ANGELICA JOANNIS JOSEPHI F KAUFFMANN… zu lesen. (siehe Ill. 11)
In the Allgemeines Lexikon der bildenden Künstler by U. Thieme and F. Becker, vol. 20 (1927), the artist is listed under Maria Anna Angelica Catharina Kauffmann, and in its digitized modern successor, the Allgemeines Künstlerlexikon Online (AKL 2012 edition), under Angelica Kauffman.
As in the Biografisches Lexikon der Schweizer Kunst (BSK, 1998), in the latest 2013 edition of the Allgemeines Künstlerlexikon Online she appears as Maria Anna Angelika (Angelica) Catharina Kauffmann (Kauffman).
She was known affectionately by her British contemporaries as Miss Angel. After her death, variants such as Angelique Kauffman and Mrs. Antonio Zucchi were also employed.