My filing does not include depreciation (Schedule E, Line 18). I can't get TurboTax Online to bring me to that line item. How can I get that added?

You cannot add depreciation expense.  You after to enter an asset and the program will calculate depreciation and populate the depreciation line with the calculated amount.  If you haven't already you need to set up your rental property as an asset.  Go back to "Rental Properties and Royalties (Sch E)" in Wages & Income and "Review" it.  As you go through the interview you will be prompted to set up your rental property as an asset.  This is essential for a rental property.