georgina bartter 's best friend has pleaded guilty to a drug supply charge .
rebecca hannibal , 19 , was first charged with supplying ecstasy to ms bartter in december but originally pleaded not guilty .
police allege she purchased the ecstasy pills from matthew forti , also 19 .
ms bartter , 19 , died from a suspected ecstasy overdose in november .
she was taken to hospital after suffering multiple organ failure .