Question: Laura Don's son wrote a libretto for an operetta composed by which conductor?

Context paragraphs:
The Merry Farmer (operetta): The Merry Farmer (German: Der fidele Bauer is a 1907 German-language operetta composed by Leo Fall with a libretto by Viktor Léon.  It premiered at the Mannheim Hoftheater on 27 July 1907 and was Fall's first major hit.

Laura Don: Laura Don (February 20, 1852 – February 10, 1886) was the pseudonym of Anna Laura Fish, an American actress, stage manager, playwright and artist whose life was taken by tuberculosis while still in her early thirties.  She wrote the play "A Daughter of the Nile", that found its greater success after her death, and was the mother of the writer Glen MacDonough ("Babes in Toyland").

Der lustige Krieg: Der lustige Krieg ("The Merry War") is a three-act operetta composed by Johann Strauss II.  The work was first performed on 25 November 1881 at the Theater an der Wien.  Its libretto was by F Zell (Camillo Walzel) and Richard Genée.  The operetta was well received at its premiere, and was performed 69 times during its first run.

Sì (operetta): Sì is an operetta in three acts composed by Pietro Mascagni to a libretto by Carlo Lombardo with verses by Arturo Franci.  The libretto is based on Lombardo's operetta "La duchessa del Bal Tabarin" and Felix Dörmann's libretto for "Majestät Mimi" set by Bruno Granichstaedten in 1911.  Mascagni's only venture into operetta, it premiered on 13 December 1919 at the Teatro Quirino in Rome.  The operetta takes its name from its central character, Sì, an actress at the Folies Bergère, so called because she could never say no.  ("Si" is the Italian word for "yes".)

The Mine Foreman (operetta): The Mine Foreman (German:Der Obersteiger) is an operetta composed by Carl Zeller with a libretto by Ludwig Held and Moritz West.  It premiered on 5 January 1894 at the Theater an der Wien in Vienna.  In 1952 the libretto served as the basis for a film "The Mine Foreman".  The operetta is rarely performed today, but the aria “Sei nicht bös” (“Don’t be cross”) has become a concert staple.

Indigo und die vierzig Räuber: Indigo und die vierzig Räuber ("Indigo and the Forty Thieves") is an operetta composed by Johann Strauss II to a German libretto by Maximilian Steiner based on the tale "Ali Baba and the Forty Thieves" from "The Book of One Thousand and One Nights".

Die Fledermaus: Die Fledermaus (] , "The Bat", sometimes called "The Revenge of the Bat") is an operetta composed by Johann Strauss II to a German libretto by and Richard Genée.

Babes in Toyland (operetta): Babes in Toyland is an operetta composed by Victor Herbert with a libretto by Glen MacDonough (1870–1924), which wove together various characters from Mother Goose nursery rhymes into a Christmas-themed musical extravaganza.  Following the extraordinary success of their stage musical "The Wizard of Oz", which was produced in New York beginning in January 1903, producer Fred R. Hamlin and director Julian P. Mitchell hoped to create more family musicals.  MacDonough had helped Mitchell with revisions to the "Oz" libretto by L. Frank Baum.  Mitchell and MacDonough persuaded Victor Herbert to join the production.  "Babes in Toyland" features some of Herbert's most famous songs – among them "Toyland", "March of the Toys", "Go To Sleep, Slumber Deep", and "I Can't Do the Sum".  The theme song "Toyland", and the most famous instrumental piece from the operetta, "March of the Toys", occasionally show up on Christmas compilations.

Prince Ananias: Prince Ananias was the first operetta composed by Victor Herbert.  The libretto is by Francis Neilson.  It was first produced by a troupe called "The Bostonians" at The Broadway Theatre on November 20, 1894, directed by Jerome Sykes.  It remained in their repertoire for three seasons and was given more than 300 performances in all.  A modest success at first, it did well on tour.

The Chocolate Soldier: The Chocolate Soldier (German title: "Der tapfere Soldat" or "Der Praliné-Soldat") is an operetta composed in 1908 by Oscar Straus (1870–1954) based on George Bernard Shaw's 1894 play, "Arms and the Man".  The German language libretto is by Rudolf Bernauer and Leopold Jacobson.  It premiered on 14 November 1908 at the Theater an der Wien.

Supporting paragraphs: Laura Don Babes in Toyland (operetta)
Answer: Victor Herbert