Tremolo was a member of female mutant terrorists. She was hired by Cyber to commit acts of extortion, and worked for a notorious drug cartel. A other member of group, Shrew eventually quit the team and agreed to testify against the cartel for immunity. Tremolo and other The Belles, upon discovering their former teammate's betrayal, sought out to kill Shrew. The government then placed Shrew under the protection of X-Factor. The Belles ambushed X-Factor in a hotel, and in the ensuing battle. She was initially driven off by Wolfsbane, and was later punched out by Quicksilver and taken  into custody with the other defeated Belles.

She is currently depowered due to events of M-Day.