Can I add $200 to an employee's direct-deposit paycheck--it's already been deposited for two days at her bank--to correct my mistake?

Hello there, @daniel69.

You can create an unscheduled payroll check to process the additional $200 to your employee. 

Since your employee's direct-deposit paycheck has been deposited already, creating an unscheduled payroll check is the option to correct it. Please take note that the only available check dates are dates that fall after your last check date and before your next payday. 

Let me walk you through the complete steps:

1. Go to the  Payroll menu.
2. Within the Employees tab, select Run payroll.
   
3. Find the employee you want to pay. Then, select Create another check.
4. Enter employee compensation, including any salary adjustments, and other pay types.
5. Confirm the pay period and check date.
6. Select Preview Payroll, and then select Submit payroll.
7. Click Finish payroll.

For more details, you can check this article: Create Unscheduled Payroll Check.

I've got an article, where you can view the complete list of available payroll reports in QBO. It includes steps about printing, customizing, and marking them as your favorite: Run payroll reports. 

Let me know in the comments if you have other payroll concerns and questions about managing employees' data in QBO. Take care and stay safe, daniel69.