Question: Which much more famous artist co-writes and sings backing vocals on Kellie Pickler's 2008 song "Best Days of Your Life"?

Context paragraphs:
Makin' Me Fall in Love Again: "Makin' Me Fall in Love Again" is a song written by Karyn Rochelle, James T. Slater, and Shane Stevens, and recorded by American country artist Kellie Pickler.  It was released in April 2010 as the fourth single from her self-titled second album.  The song is about someone being in love and still having that feeling, despite being told that it will fade away.  Pickler said that it reflected her current relationship.

100 Proof (song): "100 Proof" is a song recorded by American country artist Kellie Pickler.  It was released on April 16, 2012, and served as the second single from the album of the same name.  It was written by Leslie Satcher and James T. Slater, the same writers that wrote the album's first single "Tough".  "100 Proof" uses an analogy between love and alcohol levels, as if its addictive.  The song was Pickler's first to not reach the Top 40 on the "Billboard" Hot Country Songs chart, peaking at number 50 instead.

Morgane Stapleton: Morgane Stapleton (previously Hayes), is an American singer-songwriter and the wife of Chris Stapleton.  She performs background, harmony and duet vocals in Stapleton's band and was instrumental in the creation of his debut album "Traveller".  A songwriter in her own right, she has written material that has been recorded by Carrie Underwood, Kellie Pickler and LeAnn Rimes among others and also appeared as a background session vocalist on records by Underwood, Pickler, Dierks Bentley and Joe Nichols.

Martin Chambers: Martin Dale Chambers (born 4 September 1951 in Hereford) is an English musician, who is best known as a founding member and drummer of the rock band the Pretenders.  In addition to playing the drums with the group, Chambers sings backing vocals (lead vocals on the song "Fast or Slow (The Law's the Law)", the B-side of the singles "2000 Miles" and "Show Me", which he also wrote) and plays percussion.  He was part of the original band line-up which also included Chrissie Hynde (vocals/guitar), James Honeyman-Scott (guitar/vocals/keyboards) and Pete Farndon (bass guitar/vocals).  Hynde and Chambers are the only two surviving original members, and he has served two separate tenures with the group.

Someone Somewhere Tonight: "Someone Somewhere Tonight" is a song first recorded by Walt Wilkins on his record Mustang Island, and later by American country pop artist Kenny Rogers for his 2006 album, "Water & Bridges".  The song was later covered by Pam Tillis for her 2007 album, "RhineStoned".  In 2013, the song was recorded by Kellie Pickler and was released as the first single from her fourth studio album, "The Woman I Am".  Pickler's version peaked at number 49 on the "Billboard" Country Airplay chart in 2013.

Kellie Pickler (album): Kellie Pickler is the self-titled second studio album by American country artist Kellie Pickler.  The lead-off single, "Don't You Know You're Beautiful", was debuted at the 43rd Academy Of Country Music awards and peaked at 21 on Hot Country Songs.  The album was released via BNA Records/19 Recordings on September 30, 2008.  Since the albums' release, three more singles have charted; "Best Days of Your Life" at number 9 (which was co-wrote with fellow country artist Taylor Swift), "Didn't You Know How Much I Loved You" at number 14 (a re-recording of an album cut from Pickler's debut album "Small Town Girl") and "Makin' Me Fall in Love Again" at number 30.

100 Proof (album): 100 Proof is the third studio album by American country music artist Kellie Pickler.  It was released on January 24, 2012.  The album includes the single "Tough".  The title track, was released exclusively on iTunes on December 20, 2011.  The album sold 27,000 copies in the first week, and is the highest-charting album of Pickler's career on the "Billboard" 200 and the Digital Albums chart.

Ben Aaron: Benjamin Aaron Colonomos (born September 10, 1981) is a New York City-based media personality formerly for NBC Universal's LXTV and WNBC's "New York Live", and for the nationally syndicated "Crazy Talk" television series.  Currently he co-hosts the Scripps-produced talk show "Pickler & Ben" with country artist Kellie Pickler, which airs on Scripps stations and CMT; the show is produced out of Scripps' Nashville station, WTVF.

Best Days of Your Life: "Best Days of Your Life" is a song written and performed by American country artist Kellie Pickler, and co-written by Taylor Swift.  It was released on December 1, 2008 as the second single from her self-titled second album.  Swift also provides background vocals on the song.  The song is about a narrator explaining how her former boyfriend cheated on her and moved on to a new girlfriend to start a family with, wishing them well on their new life but says that the new girl won't top what they previously once had before.

Don't You Know You're Beautiful: "Don't You Know You're Beautiful" is a song written by Chris Lindsey, Aimee Mayo, and Karyn Rochelle (who co-wrote her previous hits "Red High Heels" and "I Wonder"), and recorded by American country artist Kellie Pickler.  It served as the lead-off single to her self-titled second album.  Pickler debuted the song at the 43rd annual Academy of Country Music Awards, and it was officially released to radio in June as the fourth single of her career.

Supporting paragraphs: Kellie Pickler (album) Best Days of Your Life
Answer: Taylor Swift