You're going to want to read up, and send to her, things like these results (google is your friend):

sep ira s corp shareholder

Such as: https://irahelp.com/forum-post/75473-sep-ira-contribution-limit-s-corp/

Because the person wears two hats: As shareholder and as employee. As employee, you have to contribute through payroll which is calendar year, so 2023 has a shut door. There are different provisions for the employer share.

And make sure to read SEP IRA, not SIMPLE IRA or Solo 401(k), unless your taxpayer is shopping for plan ideas.