If she has enough FICA tax paid on W-2 income to earn four quarters (about $6,700 for 2023), there is no need to pay more SE tax with the hope that she lives long enough to collect another $5 a year when she retires.  

I had one client, a career federal employee back in the days they did not pay Social Security tax, who needed one more year of Social Security credits in order to qualify for benefits.  Dabbled in real estate; some years she earned a couple commissions, others she did not.  So we used the Optional Method, and at age 70 she started collecting something like $45 a month.  She lived past 90.  At least it paid my fees, and an occasional restaurant meal for the rest of her life.