Filing Taxes for a deceased taxpayer

My mother in law passed away in 2022 and I'm doing her 2021 taxes.  She's getting a refund. She has a trust and my sister in law is the executor. Do I need to file form 1310? Is my sister in law considered the personal representative and are the trust documents considered the court certificate showing the appointment? What else do I need to file to make sure I do this correctly?