It appears from these facts that your cousin would have to file a claim against your father's estate in order to proceed. Since there was no estate opened because everythng was TOD, it's more likely than not that you are OK. If your cousin was concerned, she should have done something before this time. 2009 is 13 years ago.
I agree with Attorney McMahon, except for the math. This apparently happened 4 years ago. Regardless, under the facts presented, your cousin has almost no chance of prevailing. Even if she does, there is nothing that she can collect against. An attorney in Kuwait is not going to be able to do anything. She will need to hire an attorney to sue where your father lived. There does not appear to be enough money involved for her to even pursue this, but if she does, you will need to wait to see what she does before deciding how to respond. If some kind of claim is filed, I would consult with a probate lawyer on how to proceed.
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Start with where your grandfather lived when he died. Check with the Probate Court of that County to see if an estate was opened. If he was a Missouri resident at the time of his death and an estate was not opened within one year of his death, his Will was no longer effective. It would not matter what it said. All his assets would go to his children in equal shares if his wife did not survive him.
If there was an estate opened in time, the Court would not have allowed distribution to any persons unless it conformed to the Will. If the Estate was closed, your Dad was discharged as the Executor and had no further liability. There can be no claim against him or against his estate and certainly not against his children
This comment does not create an attorney-client relationship. The law and its application by the courts is constantly evolving and changing. This discussion is not to be taken as a definitive guide, and should not be relied upon to determine all fact situations. Each set of facts must be examined separately with the current case and statutory law analyzed and applied accordingly.