I am so sorry about your mother, that is so very sad.
I have always believed that I knew her murderer, but no one would ever listen to me.
I think you are right. A murder like that is usually by a person who knows the victim as 37 wounds is an expression of anger, rage.
This 'Friend' who saw her leave. Was this a male or female? Was your mother dating someone? An ex?
Don't give up. If you have not bugged the police in a while, now it a good time. There could be DNA evidence now.
Your mother would be about 61 now. The killer is probably of similar age. Would be nice to get him before time is up.