Destiny’s Child is reuniting, but it’s not exactly a happy occasion. Just ask Kelly Rowland.

We hear the singer is furious that she and former DC cohorts Beyoncé and Michelle Williams have to head to Chicago on Tuesday to face a copyright-infringement lawsuit for their song “Cater 2 U.” The reason for her anger, besides the obvious? According to a source, Rowland blames the legal mess on Beyoncé’s father – and his tactics for lining his daughter’s pockets with cash.

“Matthew [Knowles] has a long history of trying to get songwriters to add Beyoncé’s name to songs she didn’t compose, just so she gets publishing royalties,” the insider says of Daddy Knowles, who managed the group. “That information eventually became widely known, and now anyone who wants to accuse Kelly or Destiny’s Child of stealing material has ammunition to file a lawsuit. Kelly is livid.”

Indeed, Beyoncé’s songwriting credits have been publicly questioned several times. In 2006, for example, she declared she wrote the breakup anthem “Irreplaceable” “for [her] girls” – causing singer/songwriter Ne-Yo to angrily announce that he penned all the lyrics for the song, then got minimal help from Beyoncé on the melody. But even that may have been generous: Rumors swirled that B’s composer credit was added only as a courtesy.

Adding fuel to the Rowland/Knowles fire: Kelly used to employ Matthew as her manager; she terminated him in January.

“She and Beyoncé remained cordial at first,” our source says. “But things have gotten tense since Kelly griped that Matthew is the cause of this lawsuit.”

The proof? When Billboard mag recently saluted Beyoncé with a Woman of the Year award, Williams was on hand to fete her former cohort. Rowland was not.

“Kelly isn’t happy having to fight these allegations,” continues the source. “She feels as though this is just another mess that Matthew got them into while only trying to serve the sole interest of his daughter.”

Neither Knowles nor Rowland responded to calls for comment by deadline.