The rules on whether a final return needs to be filed in the year a person dies are the same as for determining if a person needs to file when they are alive, and depends on the amount and type of income the person has. You can use the IRS tool here, https://www.irs.gov/help/ita/do-i-need-to-file-a-tax-return
Basically, if your mother's only income is a social security benefit, then a return is not required. However, you will need to make sure she doesn't own stocks, or have a pension, or other retirement accounts. You sound sure, but sometimes there are surprises.
You also have until April 15, 2023 to figure everything out, and you can't file until January 20, even if you thought you were ready sooner. So take your time to process everything and relax for now. And we are sorry for your loss.
