How am I to deal with the situation?

My son & daughter in law are living with me. I, my only son ate facing mental harassment from my daughter in law from recent times. Every fortnight she picks up a quarrel with my son for no reason & goes to her native, she is working, done her BBM, my son is an engineer working for an MNC, recently my husband passed away, 8 months back, we are staying in our own house at Hubli, actually they both were residing in Bangalore, in spite of the covid situation, both of them are with me, In spite of the death of my spouse, we are in a depressed state, but my daughter in law always needs entertainment, going out, & long ride most of the time, Though once we had been to Goa, according to her demand, always she expects my son to say yes for all her plans, she has her own rules & orders & disturbs us most of the time, She has no control over her behaviour & always feels she is right & her parents also support her.Once she goes to Mysore, she abuses us & her parents are also instructing us to follow their rules which we find it a very big nuisance, most of the time threats & always keep complaining about us, keep crying most of the time, which is so disgusting, we have not taken any dowry, nor we demanded anything from them. She seems to be so stubborn by arguments, by banging her head on the wall, by cthreatening with a knife & cut her wrist so she bleeds which has taken place once. Please Sir give me a solution for all my problems, I am a Teacher in a reputed School in Hubli, recently I resigned because of my depressed state. My daughter in law says, she wants to come down, but how long she will be happy with my son, I dont know, within a week another problem starts, again she will leave to Mysore, She wants only the comforts & luxury life from our side but never want to take up a family life & responsibility. What precautions should we take in case of any mishappenings.