@jacmaw1
If you are uncertain as to how to proceed and your sister had substantial assets, you should consult with local legal counsel.
See https://www.avvo.com/probate-lawyer.html
Otherwise, note that you may not need a court appointment to be considered your sister's personal representative for the purposes of filing an income tax return on her behalf. If you are in possession of, or have control over, your sister's property, that is sufficient.
