Forced marriage of my girlfriend

I and my girlfriend has been in a relationship since 6 years now. We both are above 20 years of age. Recently her father has been forcing her to get married to some other guy because our caste do not match. She refused many times. Her parents then suddenly organised her engagement with some other person. He(fiance) is not aware of our relation. Her parents are emotionally blackmailing her to leave me and marry that man or else they will commit suicide. They keep her locked in her room so that she doesnt escape. She was third year student in a college, but her parents have stopped her studies too. Recently we had a conversation over mail in which she mentioned her condition and said that I should have taken step before but I was busy with my career. I asked to run away from there and come to me. Her dad saw that mail and now he is warning her to marry that man peacefully or else he will use those mails against me and my family for provoking his daughter. He also made her sign on some paper that I have been provoking her to run. Her mental condtion is good. One month ago she was depressed and had feeling of commiting suicide (our marriage is the reason here) so they consulted a physciatrist too. The forced signature and being locked in room part is mentioned by her in a letter and mail. I have a picture of that letter written by her. I want her to get rid of her parents and live somewhere peacefully. Even she wants the same. Kindly guide me with the legal steps that she can take and I can take seperately for her well being without a FIR or case being registered against me. Me and she both want her marriage to stop and her relationship with her family to end.