Question: Which instrument is Clara Rockmore a virtuoso of in the novel Us Conductors?

Context paragraphs:
Zip-cord: Zip-cord is a type of electrical cable with two or more conductors held together by an insulating jacket that can be easily separated simply by pulling apart.  The term is also used with optical fiber cables consisting of two optical fibers joined in a similar manner.  The design of zip-cord makes it easy to keep conductors that carry related electrical or optical signals together and helps avoid tangling of cables.  Typical uses include lamp cord and speaker wire.  Conductors may be identified by a color tracer on the insulation, or by a ridge molded into the insulation of one wire, or by a colored tracer thread inside the insulation.  Zip cords are intended for use on portable equipment, and the US and Canadian electrical codes do not permit their use for permanently installed wiring of line-voltage circuits.

Marina Piccinini: Marina Piccinini (born 1968) is an Italian American virtuoso flautist.  She is noted for her performances of compositions by Mozart and Bach, and has performed with many of the world's top orchestras and conductors.

Us Conductors: Us Conductors is a debut novel by Canadian writer Sean Michaels.  Published in 2014 by Random House in Canada and Tin House in the United States, the novel is a fictionalized account of the relationship between Léon Theremin (also known as Lev Termen), the inventor of the theremin, and Clara Rockmore, the musician regarded as the instrument's first virtuoso player.

Clara Rockmore: Clara Rockmore (née Reisenberg, March 9, 1911 – May 10, 1998) was a classical violin prodigy and a virtuoso performer of the theremin, an electronic musical instrument.  She was the sister of pianist Nadia Reisenberg.

Virtuoso: A virtuoso (from Italian "virtuoso" ] or ] , "virtuous", Late Latin "virtuosus", Latin "virtus", "virtue", "excellence", "skill", or "manliness") is an individual who possesses outstanding technical ability in a particular art or field such as fine arts, music, singing, playing a musical instrument, or composition.  This word also refers to a person who has cultivated appreciation of artistic excellence, either as a connoisseur or collector.  The plural form of "virtuoso" is either virtuosi or the Anglicisation, virtuosos, and the feminine forms are virtuosa and virtuose.

Jean-Baptiste Arban: Joseph Jean-Baptiste Laurent Arban (28 February 1825 – 8 April 1889) was a cornetist, conductor, composer, pedagogue and the first famed virtuoso of the "cornet à piston" or valved cornet.  He was influenced by Niccolò Paganini's virtuosic technique on the violin and successfully proved that the cornet was a true solo instrument by developing virtuoso technique on the instrument.

Mike Dawes: Mike Dawes is an English virtuoso Fingerstyle guitar player known for composing, arranging and performing multiple parts simultaneously on one instrument using unique extended and micro-techniques.  His debut record with CandyRat Records gained strong critical acclaim and spawned a variety world tours and singles, notably a viral virtuoso arrangement of Somebody That I Used to Know by Gotye that gained over 2 million hits on YouTube alone on its first day of release.  Dawes is also lead guitar player for Justin Hayward of the Moody Blues featuring heavily on numerous DVD and PBS releases, notably 'Spirits...Live' which debuted at #2 on the US billboard chart.

Alexander Frey: Alexander Frey is an American symphony orchestra conductor, virtuoso organist, pianist, harpsichordist and composer.  Frey is in great demand as one of the world's most versatile conductors, and enjoys great success in the concert hall and opera house, and in the music of Broadway and Hollywood.

Hans von Bülow: Baron Hans Guido von Bülow (January 8, 1830February 12, 1894) was a German conductor, virtuoso pianist, and composer of the Romantic era.  One of the most famous conductors of the 19th century, his activity was critical for establishing the successes of several major composers of the time, especially Richard Wagner and Johannes Brahms.  Alongside Carl Tausig, Bülow was perhaps the most prominent of the early students of Hungarian virtuoso pianist, conductor and composer Franz Liszt – therein performed the first public performance of Liszt's Sonata in B minor in 1857.  He became acquainted with, fell in love and eventually married Liszt's daughter Cosima, who later left him for Wagner.  Noted for his interpretation of the works of Ludwig van Beethoven, he was one of the earliest European musicians to tour the United States.

The Art of the Theremin: The Art of the Theremin is the first official album by theremin virtuoso Clara Rockmore, and the only one released in her lifetime.  It was produced by Robert Moog and his first wife, Shirleigh Moog, and was released as an LP in 1977 by Delos International Records.  As with most of her live performances, she was accompanied minimally by her older sister, Nadia Reisenberg, on piano.  The 1977 Delos LP and 1981 Japanese Delos LP release were entitled "Theremin".  The 1987 Delos CD was titled "The Art of the Theremin".

Supporting paragraphs: Us Conductors Clara Rockmore
Answer: the theremin