To claim your daughter as a dependent, she must be your qualifying child or qualifying relative. To be your qualifying child, your daughter must be less than 19 years old at the end of the year, or she may be less than 24 years old and enrolled full-time in school. She must also have lived with you for more than half the year, and she can't provide more than half of her own financial support.
In many cases, an individual who can be claimed as a dependent on another person's income tax return won't file her own 1040. However, the Internal Revenue Service sometimes requires such individuals to file, or they may file to claim a refund. Fortunately, if your daughter meets certain qualifications, you can claim her as a dependent even if she files her own income tax return.
If your daughter is too old to be a qualifying child, or if she doesn't live with you for more than half the year, you can still claim her as a dependent if she is your qualifying relative. To be your qualifying relative, your daughter must not provide more than half of her own support, and she must earn less than the personal exemption amount for the year.
If your daughter files a separate return and she meets all other qualifications to be your dependent, you can usually claim an exemption for her. However, if your daughter files a joint return, you may or may not be able to claim her as a dependent. If she is your qualifying child, you can't claim her as a dependent if she files a joint return, unless she files the return only to claim a refund and doesn't list any deductions or claim any tax credits. However, if she is your qualifying relative, you can claim her as a dependent even if she files a joint return.
If your daughter already filed a joint return and she is your qualifying child, she can't change her filing status, and you typically can't claim her as a dependent. If you qualify to claim your daughter as a dependent, she can't claim a personal exemption for herself even if you don't actually include her as a dependent on your return.