There is an on-line free and totally confidential questionnaire called the Mosaic Threat Questionnaire that you can google. Police departments, including the US Capitol Police for Congress use it to help understand if a suspect is likely to commit violent crime.
Your friend can look at it on-line, confidentially. If too many of her answers about her husband are "yes", it might help her take this seriously.
I am so sorry to hear this. It is shocking, and with her life and livelihood so entwined with her husband, this is a terrible loss and very hard to process, accept, and move on from. You are a great friend to be at her side.
ShootingStar1