Question: What singer signed a contract with Def Jam Recordings at age 19 and was mentored by LA Reid and Jay-Z?

Context paragraphs:
The Island Def Jam Music Group: The Island Def Jam Music Group (IDJMG) was an American record label group formed in 1998, combining the operations of over 14 record labels including Island Records, Def Jam Recordings, and Mercury Records.  In 2011, Motown Records was split from The Universal/Motown Records Group and subsequently became a division of The Island Def Jam Music Group.  On April 1, 2014, Universal Music announced that Island Def Jam's operations would be split between three entities: Island Records, Motown Records, and Def Jam Recordings.

Music of the Sun: Music of the Sun is the debut studio album by Barbadian singer Rihanna.  It was released on August 30, 2005 in the United States through Def Jam Recordings.  Prior to signing with Def Jam, Rihanna was discovered by record producer Evan Rogers in Barbados, who helped Rihanna record demo tapes to send out to several record labels.  Jay-Z, the former chief executive officer (CEO) and president of Def Jam, was given Rihanna's demo by Jay Brown, his A&R at Def Jam, and invited her to audition for the label after hearing what turned out to be her first single, "Pon de Replay".  She auditioned for Jay-Z and L.A. Reid, the former CEO and president of record label group The Island Def Jam Music Group, and was signed on the spot to prevent her from signing with another record label.

Def Jam Recordings: Def Jam Recordings is an American record label focused predominantly on hip hop and urban music, owned by Universal Music Group (UMG).  In the UK, the label takes on the name Def Jam UK and is operated through Virgin EMI Records, while in Japan, it is known as Def Jam Japan, operating through Universal Music Japan.  The label distributes releases of various record labels, including Kanye West's GOOD Music, Ludacris' Disturbing Tha Peace, and ARTium Recordings, headed by Def Jam's current executive vice president, No I.D..  Current artists include Iggy Azalea, Logic, Big Sean, Kanye West, Leona Lewis, 2 Chainz, Axwell Λ Ingrosso, Mother Mother, Afrojack, Jeezy, Jeremih, Ludacris, Alesso, Pusha T, Vince Staples, Desiigner and Jhené Aiko among others.

Amerie: Ameriie Mi Marie Rogers (born January 12, 1980), known professionally as Amerie (currently Ameriie), is an American singer, songwriter, author, actress and record producer.  She debuted in 2002 with her highly acclaimed debut album "All I Have".  In 2003, she helped develop the BET original series "The Center", which she also hosted, and, during her run as host, accumulated the highest ratings ever for any show in its time slot.  Amerie's time on the series was short-lived due to her landing a starring role in the 2004 film "First Daughter", alongside Katie Holmes, Marc Blucas, and Michael Keaton.  In 2005, Amerie released her sophomore album "Touch", which included her biggest hit to date, "1 Thing".  The song and the album earned her two Grammy nominations and gained her crossover recognition.  Her third album, "Because I Love It", achieved moderate international success in 2007, although it was not released in North America and she was subsequently bought out of her Sony contract by LA Reid Columbia Records' roster.  Ameriie released her fourth studio album, "In Love & War", in 2009 on Island Def Jam.

Nobody's Smiling: Nobody's Smiling is the tenth studio album by American hip hop recording artist Common.  It was released on July 22, 2014, by Def Jam Recordings and No I.D.'s label ARTium Records.  Following the release of his 2011's album "The Dreamer/The Believer", Common took a hiatus from musical endeavors.  In 2013, he returned to the studio and began working his tenth album and later revealed that the production, much like his previous effort, would be handled entirely by his longtime collaborator and record producer No I.D..  In 2014, Common signed a recording contract with No I.D.'s ARTium Records, through Def Jam Recordings, for the distribution of the album.

S. Carter Records: S. Carter Records was a record label formed by Jay-Z.  The label included Foxy Brown.  The label was formed after The Island Def Jam Music Group, holding a 50% stake in the Roc-A-Fella Records, bought the last 50% of the company.  They also appointed Jay-Z, the president of Def Jam Recordings, soon after Damon Dash and Kareem "Biggs" Burke were released as the co-founders of Roc-A-Fella Records.  Dash and Burke have started up Dame Dash Music Group since, which was also distributed by Island Def Jam.  In 2009, S. Carter Records dissolved and went out of business after Jay-Z created Roc Nation in 2008, which was actually a 10-year contract agreement between him and concert promotion company Live Nation.  Despite the closure, the name still bears copyright on later Jay-Z releases, albeit as "S. Carter Enterprises".

Unfinished Business (Jay-Z and R. Kelly album): Unfinished Business is the second collaboration album between R&B artist R. Kelly and rapper Jay-Z and was released worldwide on October 26, 2004.  It was distributed in the United States and Canada by Jive Records and Island Def Jam Music Group, by the Bertelsmann Music Group (BMG) and its subsidiary Jive Records, except in Canada and the United States of America where Island Def Jam Music Group and its labels Def Jam Recordings and Roc-A-Fella Records replaced BMG.  The album was composed of unreleased tracks from the recording sessions of 2002's "The Best of Both Worlds", although slight additions were made.

So Amazin': So Amazin' is the third studio album by American singer Christina Milian.  The album, her first studio release since 2004's "It's About Time", was released by Island Records on May 16, 2006 in the United States.  Unlike previous records, which had contributions from many producers, Milian wrote and produced "So Amazin"' primarily with hip hop producers Cool & Dre.  During production, Milian was mentored by L.A. Reid and executive producer Jay-Z of Def Jam Recordings.

Christina Milian: Christine Flores (born September 26, 1981), better known as Christina Milian ( ), is an American singer, songwriter and actress.  At the age of 19, Milian signed a contract with Def Jam.  In 2001, Milian released her self-titled debut album, which featured the singles "AM to PM" and "When You Look at Me"; "AM to PM" charted within the Top 40 of the U.S. "Billboard" Hot 100 and both peaked in the top three on the UK Singles Chart.  In 2004, Milian released her second studio album "It's About Time", which provided her first major U.S. hit, "Dip It Low", which reached number five on the U.S. "Billboard" chart. " Whatever U Want" was released as the album's second single.  Both singles charted within the Top 10 of the UK chart.

Sail Out: Sail Out is the debut extended play (EP) by American recording artist Jhené Aiko, released on November 12, 2013, through Def Jam Recordings.  It will be Aiko's first release under the label after leaving her contract with Sony Records in 2003.  After leaving Sony Records, Aiko released her first mixtape "Sailing Soul(s)" (2011), independently; the mixtape featured appearances from well-known artists and was met with generally positive reviews.  In 2012, Aiko met with American record producer and vice president of A&R at Def Jam No I.D., who ended up signing Aiko to his Artium Records imprint, through Def Jam.

Supporting paragraphs: So Amazin' Christina Milian
Answer: Christina Milian