Possible Withheld Inherence

My mother passed in 2003, I was a minor at the time. I recently reconnected with her best friend whom I hadn't spoken to since around the time she passed. She asked if I ever got my mother's money she had left me, I told her how much my father gave me and she said my mom was worried about my father not taking care of me in the event of her passing and told me I should have had $100k coming to me. She also told me she had put her own house up as collateral for my father to distribute the estate.

When my father gave me the money he did give me he told me he was supposed to wait until I was 21 but he didn't see the point in waiting and gave it to me when I was 18. It wouldn't surprise me if he had kept as much as he saw fit. I had laughed it off as typical of him, but my husband says I should see if I can get what I was meant to have.

How do I find out the details of the estate to know if that money was there for me? Is there even anything I can do this many years afterwards or is it too late? We're in the US. Thank you for any insight.