How can I help my mother n law??

My sister n law passed away at the very young age of 28 from a disease called Steven Johnson's Syndrome. This of course majorly impacted the entire family. But no one is as affected as my mother n law. My mother n law and I are very close. Practically best friends. I try to talk to her when she feels down. But here lately her sadness has turned into anger. Her husband, my husband, my children, and I have all have to deal with her anger issues. I completely understand that she is angry and I just wish there was a way I could help her.

What I want to know is how do I convince her to seek professional help. She has not seen a counselor at all since my sister n laws death. I know she really needs it. I have told her how much seeing a counselor has helped me and my bipolar disorder. I realize that what I am going through is not the same as what she is going through. But I know how seeing a professional can make a difference. How do I talk to her about this? How can I make her understand that we all miss my sister n law; but there is nothing else we can say or do to help her feel any better. I am very worried about her.

She is angry, forgetfull, she does not pay attention while driving. I am almost afraid for her to take the kids anywhere alone. I don't want her to have to suffer any more and not only that; but we are all having to deal with her. And we need some guidance on how to help her.

Thank you so much.

Perhaps her husband, your husband and you could sit down with her to talk about your concerns?