I think it's very normal for a grieving mother who has buried her young adult son to behave irrationally. Her anger has to go somewhere even if it's not the right place. She has a lot to come to terms with. Maybe you could help her find a therapist or a support group. The group Compassionate Friends comes to mind. There are also on line grief support called Grief Net. A local funeral home might have grief resources on their website.

As for your friendship,only you can make that decision. I might try to point her towards help before I broke up the friendship

Hope this helps