How do I find the schedule RS?

If your mother receives her retirement from the Mississippi Public Employees' Retirement System, the income would appear to be excludable as payments from a Defined Benefit Retirement Plan in accordance with IRC 414(j).  If this isn't the source of her retirement income, you might check with her plan administrator to make sure she qualifies.  See Income Exempt from Alabama Income Taxation. 

That said, to get to the relevant section in TurboTax Online: 

1. Select Tax Home in the left pane
2. On the  Hi, let's keep working on your taxes! screen, select the dropdown on the right side of the State Taxes box, then select Start, Continue, Pick up where you left off, or Review/Edit
3. If you land on a Alabama interview page, select Let's get started, Continue or other similar prompt.  Otherwise, in the left pane, select Prepare State, then proceed through the Alabama screens
4. If you've entered retirement income in the federal portion of TurboTax, you should come to the About Your Retirement Distributions page
5. Select  Edit to the right of the relevant retirement account
6. On the  Alabama Special Handling of This Distribution screen, select Yes
7. On the Reason for Exempt Distribution screen, select Defined Benefit Plan IRC 414(j) in the dropdown menu, then select Continue
8. On the  About Your Retirement Distributions screen, you should see that the income is non-taxable in Alabama.  Select Done