I already filed my 1040. I need to file a second 1040 for my teenaged daughter. How can I file this 1040 on her behalf through my account?

[DoninGA]

Using the TurboTax online editions you can only complete one tax return per account and User ID.  You would need to create a new account and a new User ID for another tax return.

Go to this TurboTax website and click on Sign up in the upper right of the page to start a new account - https://turbotax.intuit.com/personal-taxes/online/file-your-own-taxes/

[Vanessa A]

You cannot.  You will need to create a second account for your daughter.  You can only file one return per account.