If she is a full time student under the age of 24 then you should be able to claim her as a dependent under the Qualifying Child rules if she meets all the requirements. Her income is not a factor under the QC rules.
If she had taxes withheld from her income then she should file a tax return to get the taxes refunded. If she does file a tax return make that she indicates on her tax return that she can be claimed as a dependent. If she was self-employed and received a Form 1099-MISC or cash and it was $400 or more then she is required to file a tax return reporting her self-employment income and expenses on Schedule C of a personal tax return, Form 1040.
To be a Qualifying Child -
1. The child must be your son, daughter, stepchild, foster child, brother, sister, half brother, half sister, stepbrother, stepsister, or a descendant of any of them.
2. The child must be (a) under age 19 at the end of the year, (b) under age 24 at the end of the year and a full-time student or (c) any age and permanently and totally disabled.
3. The child must have lived with you for more than half of the year. Temporary absences while away at college are considered living with you.
4. The child must not have provided more than half of his or her own support for the year.
5. If the child meets the rules to be a qualifying child of more than one person, you must be the person entitled to claim the child as a qualifying child.
6. The child must be a U.S. citizen or U.S., Canada or Mexico resident for some portion of the year.
7. The child must be younger than you unless disabled.
