Co-own property with mother and she died WITH A JUDGEMENT AGAINST THE HOUSE, SO AM I RESPONSIBLE TO REPAY?

If she did not have a will, then I am assuming that the house passed to you because you owned the house with her jointly.  You will have to wait until the time when you try to sell the house to determine if the judgment still exists.  Some judgments expire, and some do not.  At the time of the sale of the house, a judgment search will be conducted and if the judgment shows up, but your mother is deceased, and no one is the executor of her estate, because nothing was probated, then you may not be responsible for paying it off.