A: The liability of the law firm could depend on a number of factors that are not revealed in your question: The nature of the mistake and how it occurred. Any complicity in the mistake by your mother. How long ago this happened. The relationship between the firm and the attorney. If you haven't, you should talk to the law firm and them if they are going to correct the mistake. If you do not get a satisfactory response, you should consult with an attorney so he or she can review all of the facts and determine if there is any basis for liability on the law firm.
A: There is no time limitation on when a will may be admitted to probate. There is no statute specifically related to nurses that I am aware of. There is a general statute concerning wills obtained under duress, fraud, or undue influence. It is difficult from your description to determine what the status of the case is and whether there was ever a final order. The finality of a decree depends upon a number of factors not disclosed by your description. Since this appears to be an ongoing case, questions could be addressed to the attorneys in the case who would be more familiar with the facts.