You are correct, you cannot use the Maximize function in TurboTax for your wife's solo 401(k) contribution if she also made elective deferrals to another employer's plan. You have correctly calculated her maximum elective deferral to the Solo 401(k) plan. After entering the $14,400 as the elective deferral to the solo 401(k), you can use the Maximize function for a SEP plan to calculate the maximum employer contribution to the solo 401(k).
