I am concerned when my sister had power of attorney over my father during his death and when the documents were signed and notarized.

Did he have a will and is she Executor? Because once a person dies, the POA in no longer is in effect. The Executor takes over. He/she probates the will and must either mail it to beneficaries/interested parties or make it available. At that time, you can ask for an accounting of how money was spent under the POA.

Why do you want this information? What are you planning to do with it?