Marriage with legal witness for no suicide later

I was in relationship with a girl for two years now. I had clearly conveyed that the marriage is something I will be interested if my financial situation improves to take care of her and mine. At the start she was okay with it, and involved in sexual relationship consensualy. She herself initiated the sexual activities, however after one year she started impressing to get married as she is 2 years older than me (35 F). In recent times multiple times she had threatened me to commit suicide and started harrassing me in work. She damaged her career as well as mine. My family and I, out of fear to get imprisonment are now ready for marriage despite of my will as she downed her character in my eyes by her behaviour of social agony, erratic actions, self harm and suicidal threatening. I want to know, is there any legal way, that before marriage we could get something in written record in presence of police authorities that if is she does something in future, me and my family will not be responsible by any sort? I don't trust her at all now, and I want some security to go ahead. I fear that if I press her any more she will commit something and thus ready to take things for her will.