mother recently passed away procedure to set up probate and steps to determine life insurance policy under WA state probate law

There are hundreds of life insurance companies. I would start by going through her personal effects to find a policy. Check with her bank to see if she had a safe deposit box. You could call AARP, a common provider of insurance policies to the retired community. You might also see if there is a way to access her credit report. Some insurance companies will do a credit check for policies over a certain amount. Also check with any of her advisors: attorney, CPA, stock broker. you could then start with companies who have agents in her neighborhood.

If you can find all of her cancelled checks or credit card bills, sort through them to see if any premiums were paid. Then contact the company with proof of such payment and see what happens.