Filing first self assessment as UK resident but non UK citizen

Hello, asking this on behalf of my wife who is retired US citizen and now resident in UK on spouse visa. She will not work in UK. All income is US sourced pension/ Social security. We applied for a UTR using form SA1 which we posted to HMRC and received back her UTR several days ago. We are not sure what steps to take next. We tried to create an individual account with HMRC but as she does not have a NI number the process stalls. Wondering how best to navigate this. She will be a UK tax resident for 2023/24 so we do have some time before needing to file. Appreciate any advice regarding next steps. Thank you.

Hi Brian Courtney,
As you already have the UTR, this will enable you to file the tax return to declare the foreign income.
Tax on foreign income
Thank you.