Since she is not related to you, to claim her as a dependent on your tax return she must have lived in your home for the entire year.  Since she did not, you do Not enter her as a dependent on your tax return.

Yes. I did already discover that, and she was not claimed on my return.  On her return it asks for a Custodial Parent because she is under the age of 24.  Do I qualify as a Custodial Parent even though I have no legal guardianship?

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@cebax wrote:

Yes. I did already discover that, and she was not claimed on my return.  On her return it asks for a Custodial Parent because she is under the age of 24.  Do I qualify as a Custodial Parent even though I have no legal guardianship?

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Why is she filing a tax return?  Did she earn income and have taxes withheld on a W-2 so that she will be receiving a tax refund?  Or did she have self-employment income of $400 or more?

No, you are not the Custodial Parent.  The custodial parent is who the child lived with for over one-half of the year.