What can I do if my sister is not giving me my share of our father's financial estate?

A power of attorney lapses on the death of the principal (your father). In Ohio, what you need to do is open your father's estate in the probate court of the county where he resided. As part of this, you would nominate yourself to be his executor and notice would be given to your sister (and any other siblings). Do not (for God's sake) get in a contest with your sister over who should be the executor, the judge might settle it by appointing an "independent" executor, usually a crony of the judge, he or she will bleed the estate dry with huge legal fees.

Powers of attorney terminate on the death, therefore she would not have the power to act on behalf of your father's estate unless she was appointed executor in his will and she had authority from the court. If she used the power of attorney to wrongfully take assets, you may have a cause of action against her for your share of his estate. I would recommend that you speak with an attorney to discuss this matter and the options you may have.