Navy FCU Bank Account Or Service Complaint

Navy FCU Bank account or service department,

Savings account Deposits and withdrawals New York

My sister has removed money from her N.F.C.U. account without her permission or mine. I was wondering why they can not put a hold on the account where she put the money and to take LARGE sums of money without check with me or my mother?? She has removed about $72000.00 from my mom 's accout without permission and they are saying she has the legal right!!! I will sign any papers you wish to check her accounts like a lawyer would make me sign to check accounts!!