Courtney Sipes was killed while crossing a street in Smithtown on Nov. 24. Prosecutors say Lambert was driving 60 mph in a 30 mph zone.
Suffolk County District Attorney Thomas Spota said upgraded charges were presented to a grand jury after a witness said he was with Lambert when she used heroin. Prosecutors said toxicology reports showed Lambert had a heroin byproduct in her system.
Legal Aid lawyer Donald Silverman says the defense is still investigating the allegations.
The previous top charge against Lambert was leaving the scene of an accident.