It would probably be much easier on you and your daughter if her mother and stepfather kick her out. Your daughter refusing to remove the gauges is an indication that she wants to leave. So, if it happens, go pick her up and move her in with you. But be forewarned; pick your battles with teenagers. Having helped to raise two of them, (a girl and a boy), gauges, going Goth, piercings, and tattoos are trivial. Save your fight for alcohol abuse, birth control, drug abuse, and eating disorders.
My stepson wore HUGE gauges in his ears. It looked like shit, and I worried about infection. But he removed them when he got tired of them, and seven years later, his earlobes are fine.