Matilda,
OK, for your sister, you will sign as Personal Representative. Let's go back to what the IRS 1040 instructions tell us (https://www.irs.gov/pub/irs-pdf/i1040gi.pdf):
"If a taxpayer died before filing a return for 2022, the taxpayer's spouse or personal representative may have to file and sign a return for that taxpayer. A personal representative can be an executor, administrator, or anyone who is in charge of the deceased taxpayer's property. If the deceased taxpayer didn't have to file a return but had tax withheld, a return must be filed to get a refund. The person who files the return must enter “Deceased,” the deceased taxpayer's name, and the date of death across the top of the return. If this information isn't provided, it may delay the processing of the return."
The instructions later refer you to Tax Topic 356 (https://www.irs.gov/taxtopics/tc356) which further confirms and enlarges. As you are planning have any refund applied to the 2023 taxes, there would be no need for form 1310.
Lastly, do download a copy of IRS Publication 559 (https://www.irs.gov/pub/irs-pdf/p559.pdf) which I found extremely useful after my mother died without a will and I was in charge of handling her affairs.
