I am a New York lawyer. Often times credit unions have their own rules about designated beneficiaries that differ from the traditional designated beneficiary. I just had a situation where a credit union in brooklyn refused to distribute to a designated beneficiary becuase the beneficiary was not a member. However, after much back and forth with the legal department of the credit union, they distributed. If the amount warrants it, I suggest retaining counsel to file a petition compelling a turnover to you by the estate. It is key to get the credit union on your side and to have your laawyer notify their lawyer that they will ultimately be held liable if you do not get the funds. Get copies of the designated beneficiary paperwork on file with the credit union and bring it to a lawer if the value warrants it.
Does your aunt have any outstanding debts? "Naming a beneficiary for your bank or stock accounts has no bearing on the rights of creditors or the IRS. Although you've designated a new owner, the executor of your estate must still pay all of your estate's outstanding debts and expenses. If necessary, the beneficiaries may have to use some of the accounts' assets toward that end. "
Perhaps the administrator is keeping the money in the estate to pay any outstanding debts.
This answer does not constitute legal advice and no attorney client relationship has been formed. Before choosing a course of action, it is always advisable to seek the advice of an attorney in your area.