Tamira Mobley, of Wood-Ridge, met 22-year-old college freshman Tamara Blaine at Manhattan's Liberty Inn Hotel in July of 2013. Emergency responders were called to the scene some time later, to find Blaine barely conscious.
Police say Mobley said only that Blaine had had a seizure. She was pronounced dead at a hospital.
Her death was ruled a homicide after the medical examiner determined she had been injected with silicone which went into her veins.
She reportedly pleaded guilty in exchange for a lighter sentence and faces 1 1/3 to 4 years in prison.
(The Associated Press contributed to this report)