I need advice on helping my Mother In Law through the grief of losing her husband.

A little back story... He was gay and had cheated on her many many times over the 30 years they were married. They have 2 adult biological kids and 4 adopted kids. Her children had started to see stuff that is inappropriate for kids to see so she had decided to finally divorce him. My husband found him dead the next day after she had took the kids and left. There were a couple notes that he wrote before he passed.

My mother in law has blamed herself over and over and she is getting more and more depressed. We tried counseling but it didnt work with that one and I haven't been able to get her to see someone else. She has been absent from helping her kids through this grief and a lot of the load has been put on my hubby and I. I need advice on how to help her out of the black whole she is in. I love her dearly and I hate to see her this way. Please no ugly comments, just advice. I guess Im just afraid that if she gets anymore depressed that I will lose her as well.