Lisa Robin Kelly, best known for her portrayal of Eric’s sexy older sister, Laurie Forman, on That '70s Show, went into cardiac arrest and died in her sleep last night at a California rehab center. The 43-year-old actress had voluntarily checked herself into the facility to combat an alcohol addiction. "She had been fighting demons for a while and finally lost her battle," her agent said. Kelly had struggled with alcohol for years; she had been arrested multiple times for DUI and assault and reports have detailed a tumultuous relationship with her estranged husband Robert Gilliam. Sources tell TMZ that a fight with Gilliam set off her most recent relapse.