my daughter is 20,she is a college full time student, she earned $15000 last year, I paid her half expenses,why she cannot count my dependent?

If your daughter meets the qualifying requirements of a qualifying child or a qualifying relative, then you can claim her as a dependent. Below you will find the basic qualifiers: 

To determine if the individual is your qualifying child, the following questions must be true:

• The child must be related to you. 
• The child can’t be claimed as a dependent by someone else. 
• The child must be a U.S. citizen, resident alien, national, or a Canadian or Mexican resident. 
• If the child is married, they can’t file a joint return with their spouse. 
• The child must be under the age of 19 (or 24 for full-time students). 
  • No age limit for permanently and totally disabled children. 
• The child must have lived with you for more than half the year (exceptions apply). 
• The child didn't provide more than half of their own support for the year. 

If all of your answers are yes, then you may have entered something wrong when you entered her information. 

To edit your dependent in TurboTax:

1. For TurboTax Online, go to the Personal profile screen.
2. For TurboTax Desktop, open your tax return and select Personal Info
3. Select Edit next to your dependent
4. Review your answers as DoninGA described above.

 Please review the TurboTax Help articles; Who can I claim as my dependent? and Rules for Claiming a Dependent on Your Tax Return.