Check the time of death on your mother's death cert to see if she indeed survived your grandmother. Also, have qualified counsel review the will as many wills have boilerplate language requiring that a beneficiary survive a particular amount of time (e.g. 30 days) in order to take under the will. Next, assuming your mother was indeed entitled to take under the will, an estate will need to be set up for her and a fiduciary appointed who will then have authority to bring an action regarding grandmother's estate. The first step would be to compel an inventory and accounting, and next an action to remove the executor if wrongdoing is found.
I would suggest you contact legal counsel in GA to discuss your case further.
Peter Frasca practices law in Massachusetts and provides general answers on avvo for educational purposes only and does not enter into an attorney-client relationship by doing so. You are advised to provide all relevant facts and to retain legal counsel before relying on any answer expressed herein.