Question about an deceased parent that I had no contact with

My estranged mother recently passed away. I haven't spoken to her in almost 10 years for reasons I won't go into here. At one point we had a joint checking acount that her SS and an annuity were deposited in monthly. AFAIK that account is still active. I believe that joint accounts are not part of the estate. I would like to close that account. Because of her decline health a conservator was appointed for her by the Probate Court. What is my next move? Am I in liability here if someone doesn't cancel her SS and takes the money out of that account?