She's using the threat of suicide as emotional manipulation. Try and feel sorry for her as this is nothing more than a desperate attempt at control when she can't manage her emotions. She is unlikely to ever act on this threat but she definately needs help. This is actually your father's role but he would need to assert himself. In the US, a threat of suicide means an automatic 72 hour hold for a mental health assessment. Not sure about where you are but you might try asking her open ended questions next time she threatens. Suggest that since her threat is so alarming that you need to take her for emergency help and assessment. In other words, call her bluff but in a helpful way. Playing therapist is beyond your pay grade and you cannot help beyond support for seeking treatment for her. Continue to live your life and put strict boundaries on how much you will involve yourself.