Question: What is the nationality of the librettist of A Bayou Legend?

Context paragraphs:
A Bayou Legend: A Bayou Legend is an American opera composed by William Grant Still, with a libretto by his wife and frequent collaborator, Verna Arvey.

Don Giovanni Tenorio: Don Giovanni, o sia Il convitato di pietra , also known as Don Giovanni Tenorio because the title character is played by a tenor and the opera appeared the same year as Mozart's version, (English: "Don Giovanni, or The Stone Guest") is the most famous opera by the Italian composer Giuseppe Gazzaniga.  It belongs to the genre of dramma giocoso and is in one act.  "Don Giovanni Tenorio" was first performed at the Teatro San Moisè, Venice, on February 5, 1787.  The libretto, by Giovanni Bertati, is based on the legend of Don Juan as told by Tirso de Molina in his play "The Trickster of Seville and the Stone Guest" (c. 1630), leading to comparisons with Mozart's "Don Giovanni", which had its premiere later in 1787.  Mozart's librettist, Lorenzo Da Ponte, certainly knew the earlier opera.  Gazzaniga's work is much shorter than Mozart's, however, and originally formed part of a double-bill with another piece, "Il capriccio drammatico".

Verna Arvey: Verna Arvey (February 16, 1910 – November 22, 1987) was an American librettist, pianist and writer who is best known for her musical collaborations with her husband William Grant Still, a musician and composer.

Creature (2011 film): Creature is a 2011 American monster movie directed by Fred M. Andrews, based on a screenplay written by Andrews and Tracy Morse.  The film is set in the Louisiana Bayou, where a group of friends discover a local legend and are in a fight for their survival.  The film opened in theaters on September 9, 2011, in the United States and Canada.  It stars Mehcad Brooks, Serinda Swan, Amanda Fuller, Dillon Casey, Lauren Schneider, Aaron Hill, Daniel Bernhardt, and Sid Haig.  It made headlines for its low gross.

Supporting paragraphs: A Bayou Legend Verna Arvey
Answer: American