First, I'm sorry for your loss.
As far as filing Federal tax returns are concerned, this all depends upon which state you are living in. We need to first qualify you as Legal Executor. If you have already done this, and you are qualified by her Will and state statute, you needn't concern yourself with Probate Court proceedings. If your mom had no lawful spouse upon her passing, you could certainly proceed on your own without State intervention. If the estate is substantial or complex by your measure, you may consider representation unless there are no other beneficiaries or simply if you do not wish to take this task upon yourself. You shall file her return as normal and not denote as this would be her last filing. As long as she was living through 11:59pm in your time zone on 12-31-22, she (you forward) would file as usual. When you file her 2023 return, which you can do at the beginning of next year (2024), you will file 2023 as the last return.
If you are indeed your mom's executor and am also a survivor with inheritance potential, please be extra careful with your records such that another surviving beneficiary cannot challenge your actions. This is where Probate Court protections become beneficial. I wish you the best.
