My daughter made an honest mistake and clicked no one can claim her.

If she filed her return and it was rejected: To change the issue so that her return will be accepted, she will need to go in to correct her rejected return. Then, she will go back into her return (following the fix a rejected return instructions) and find her name in the Personal Info section. Click to edit beside your name. On the following screen near the bottom, you will find the area to click that she can be claimed as a dependent by someone else. I will attach a screenshot of that area, so she is better able to locate it.  

To correct a rejected return, please see the following TurboTax FAQ:

https://ttlc.intuit.com/replies/3302275

If she has already filed her return, and it was accepted: She will need to amend her return, once it has been accepted and any refund due has been paid out.  Then, she will go back into her return (following the amend instructions) and find her name in the Personal Info section. Click to edit beside her name. On the following screen near the bottom, she will find the area to click that she can be claimed as a dependent by someone else. I will attach a screenshot of that area, so she is better able to locate it.  

Please see the following TurboTax FAQ for instructions on how to amend your 2016 tax return in TurboTax.

https://ttlc.intuit.com/replies/3288565