First, if your wife's business uses the cash method of accounting, amounts received in 2024 are 2024 business income, not 2023 business income.
Second, the maximum solo 401(k) contribution in this case is net profit minus the deductible portion of self-employment taxes. For a self-employed individual with net profit of $11,500 and who does not have compensation from another employer that would result in compensation reaching the Social Security wage base, the maximum deferral to the solo 401(k) would be $10,687.
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