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?

You will need to find an elder law attorney who specializes in financial fraud in the state your father lived/died in (because each state's laws can vary) AND you will need to have some actual hard proof in order to analyze if you have a case. An ethical attorney will be honest about taking on a case that has no merit or win-ability. It will cost about $250-$300 for a 1-hour consult. Do you have the funds to pay to prosecute your case to the end? It can be many thousands of dollars, and very possibly much more. If your relationship with your sister was already crap, then you have nothing to lose.