If your wife started earning self-employment income in September, 2025, her first estimated payment would be due January 15, 2026.
Turbotax does not include the function of calculating estimated payments. There are some online calculators, or it may be a built in function of business software like Quickbooks. Remember that she will owe 15% self employment tax plus income tax (probably 12-22%) on the net income (profit after expenses) so don't forget to include expenses in your calculation.
Yes, if you increase your job withholding to cover the estimated taxes, that will also satisfy the IRS without the need to make a separate payment. You will have to do some experimenting with the withholding calculator to see how to make that adjustment. (For example, if your wife expects to earn a net profit of $4000 per month, how should you adjust your withholding to have an extra $1500 taken out of your paycheck?)
https://www.irs.gov/individuals/tax-withholding-estimator
