What kind of insurance money was this? If it was a policy that named your stepmother as beneficiary then she is likely entitled to the money.
This answer should not be construed as creating an attorney-client relationship, and is for informational purposes only.
Attorney Criscione is correct. If your step-mother was named as sole beneficiary on the policy, then she would be entitled to the entire proceeds to do with as she pleases. Benefits of insurance policies are payable only to the named beneficiaries. If there are no named beneficiaries, then it would have passed to your father's estate and the proceeds would have been paid to the intestate heirs.
If your concern is that she was not the sole beneficiary or that she took the money improperly from the estate, then I would advise that you retain an attorney. To offer a complete answer, any attorney is likely going to need much more information.
I completely agree with Attorney Martinez. If your step-mother was the beneficiary of the insurance policy she was free to spend the money any way she wanted.
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