E! News has learned that the young woman involved in the altercation with the Disney star was Alex Welch, and she has quite the résumé.
The 21-year-old hoofer, who goes by the stage name B Girl Shorty, is well known in L.A. dance circles. She appeared in Justin Bieber's "Somebody to Love" video and has danced for Miley Cyrus and Pink, appeared in Step Up 2 and was part of the runner-up team on season three of MTV's America's Best Dance Crew. She is still in South America with the Jonas Brothers.
Attempts to reach Welch and her reps were unsuccessful.
Lovato's camp, meanwhile, has no comment on either the identity of the girl or the altercation itself.
Without specifically naming the victim, a Lovato insider tells E! News that Demi confronted the backup dancer last Saturday in an altercation that led to Demi entering a treatment facility for unspecified "issues."
The source says that Lovato believed the dancer had "ratted [Demi] out" about her partying to the Jonases' dad, Kevin.
A second eyewitness tells E! News that B Girl "did not hit her back, was totally clueless."