find if mother had insurance policy and who was beneficiary

my sister was poa for my mother when she was alive. My mother passed and my sister qualified as executor. we have uncovered numerous misdoings that my sister did while poa and seems to be covering up these potentially criminal offenses now as executor. We know our mother would have had an insurance policy on herself (she had one on each of her children while growing up and was adimit about having a policy). Our sister states there was not one. Our mother had advanced dementia for the past 10 years and we've discovered that in the past 2 years of her life my sister changed over several things to include my mother's checking account to show it as a joint owner with right of survivorship. My mother was in no mental condition to sign such a thing. We think my sister may have cashed in a policy on my mother or somehow changed her to be the beneficiary. we have asked for documents but been denied by the estates attorney. How can we find if there was an insurance policy in my mother's name and who the beneficiary was (and if it was claimed).