Blackmailing is a serious crime. Blackmailing is the act of forcing someone to do or pay for something by threatening to reveal a secret. Blackmailing can possibly fall under the categories of Criminal Intimidation or Extortion, both being punishable offenses under the Indian Penal Code 1860. Blackmailing can be Criminal Intimidation under Section 503 of the Indian Penal Code, 1860. You can surely talk to her and try to stop her but if she doesn’t reciprocate well. Then, you should immediately go to a nearby police station and file an FIR against your girlfriend.