"She Ain't You" is a mid-tempoR&B, pop-flavored ballad, featuring electronic and calm beats. The song is set in common time with a moderate tempo of 92 beats per minute. It is composed in the key of D major with Brown's vocal range spanning from the note of B3 to the note of B5. It also makes use of the drums. "She Ain't You" contains a portion of a remixed version of SWV's "Right Here" (1993), which in turn samples Michael Jackson's "Human Nature" (1982). According to Najah Goldstein of WNOW-FM, it is "reminiscent of a 90's R&B love song." According to Scott Shetler of AOL Music, on the song, "Brown sings that he's found a new girl, but he's not happy because he still prefers his ex." Hannah Ash of The Harber Herald noted that the line: "With you I had a bad romance", could be a reference to Lady Gaga's 2009 single "Bad Romance". Ash also noted that the song contains "slow and pouty vocals."
Sarah Rodman of The Boston Globe wrote that the song "is totally shameless and completely effective" as it "derives much of its charm from a hefty sample of Michael Jackson's 'Human Nature'". Joanne Dorken of MTV UK wrote that the sample gives "the tune an instant eighties feel". Najah Goldstein of radio station WNOW-FM wrote that the song is "shows a much softer side of Chris Brown", and further added that it's "definitely a song for the ladies ... maybe even for pop star Rihanna." Margaret Wappler of Los Angeles Times wrote that "the sentiment of the song is refreshingly complex." Hannah Ash of The Harber Herald wrote that on F.A.M.E., "She Ain't You" and "Up to You" are "the perfect sweet and cute love songs". While reviewing the album, Sean Fennessey of The Washington Post wrote that "a more appropriate application appears on 'She Ain’t You', which interpolates Michael Jackson's 'Human Nature'. Jackson has long been the emotional, physical and musical forebear to Brown. But on 'She Ain’t You' he begs the comparison, and it isn’t pretty." Jon Caramanica of The New York Times wrote that Brown "has a really charmless way with a lyric, as on 'She Ain’t You'—"When I'm with her it's only 'bout the sex / With you I had a bad romance / And if I could just trade her in I would"—and a voice nowhere near strong enough to make up for it." The song was nominated for Song of the Year at the 2011 Soul Train Music Awards, and Top R&B Song at the 2012 Billboard Music Awards.
In the issue dated April 2, 2011, "She Ain't You" debuted at number 75 on the US Hot R&B/Hip Hop Songs chart. The song peaked at number five in the issue dated June 18, 2011, and spent twenty-two weeks on the chart. In the issue dated April 30, 2011, "She Ain't You" debuted at number 90 on the US Billboard Hot 100 chart, and peaked at number 27 in the issue dated August 6, 2011. Even though the song was only officially released in the US, it still managed to chart in other countries. On the Australian Singles Chart, "She Ain't You" debuted at number 34 on June 13, 2011, and peaked at number 27. The song was certified gold by the Australian Recording Industry Association (ARIA), denoting sales of 35,000 copies. On the New Zealand Singles Chart, "She Ain't You" debuted at number 37, peaked at number 27, and spent a total of seven weeks on the chart. In the United Kingdom, the song debuted at number 90 on the UK Singles Chart dated October 15, 2011, and peaked at number 53 on November 12, 2011. It also charted on the UK R&B Singles Chart, where it peaked at number 17.
Brown's tribute to Michael Jackson was praised by critics.
The music video for "She Ain't You" was directed by Colin Tilley, and premiered on May 2, 2011. Throughout the video, Brown pays tribute to Michael Jackson, and as stated by Lewis Corner of Digital Spy, "Brown has also choreographed a selection of iconic Jackson-inspired moves for the song's dance routine." The video opens with the following dedication, "Dedicated to my biggest inspiration of all time ... I Love You. R.I.P. Michael Jackson. 08/29/58 – 06/25/09." Brown then appears in a 1980s-styled white suit and a black fedora, performing choreography with male and female dancers against a wall of neon lights. Brown's outfit was noted for its similarities to the one Jackson wore in his music video for "Smooth Criminal" (1988). In between these scenes, Brown can also be seen wearing a black suit while dancing in front of a backdrop of dark clouds. Amber Streeter and Brown appear separately during the song's chorus where they are surrounded by gold butterflies. More scenes of Brown performing choreography are shown during the second verse. He also appears outdoors splashing in a pool of water. The video ends showing Brown flying through the air.
A writer for Rap-Up wrote that the video showcased what Brown does best – "dance". Anthony Osei of Complex magazine wrote, "If anyone can do a great Michael Jackson tribute, it's Chris Brown." A writer of DesiHits wrote that the video brought the "same magic" from his tribute to Jackson at the 2010 BET Awards, and added that it included "great lighting and even better choreography." Robbie Daw of Idolator found the video "mildly enjoyable". Brad Wete of Entertainment Weekly called Brown's dancing "tremendous" and wrote, "You'd be hard pressed trying to find a singer out there with enough dancing abilities to even attempt a proper Jackson tribute. Brown is one of the few—if not the only." At the 2011 Soul Train Music Awards, the video was nominated for Best Dance Performance.
On June 26, 2011, Brown performed "She Ain't You" along with "Look at Me Now" and "Paper, Scissors, Rock" at the 2011 BET Awards. The performance started off with Brown performing "She Ain't You" in a gray suit with voluminous pant legs and a cape fashioned out of a jacket. He then switched his outfit to a black jumpsuit and performed "Look at Me Now", as a group of dancers in similarly street black hoodies joined him on stage. Busta Rhymes later appeared from a brightly lit cube flanked by dancers in eerie, transparent masks illuminated by blinking lights. Brown ended the performance with "Paper, Scissors, Rock". On July 15, 2011, Brown performed "She Ain't You" in front of an audience of 18,000 people at the Rockefeller Plaza in New York City as part of Today concert series. For the performance, Brown wore a white shirt and a black and gold vest with black pants. "She Ain't You" was added to the set list of Brown's F.A.M.E. Tour in North America.
^Chris Brown, Andrew John Watkins, Jason Boyd, John Bettis, Steve Porcaro, Brian Alexander Morgan, Kevin Mccall, Ryan Buendia (Composers and Lyricists) (2011). "Chris Brown – She Ain't You Sheet Music (Digital Download)" (Musicnotes|format= requires |url= (help)). Musicnotes.com. Sony/ATV Music Publishing. MN0096696 (Product Number).Missing or empty |url= (help);|accessdate= requires |url= (help)