Possibly, depending on if she filled out her return properly.

With her income level being $4,500 (earned income) for the year, she could qualify for Earned Income Tax Credit.  This is a credit that is also refundable.  So if the credit brings your sister's taxes to zero, she could still get money, to the credit limit of $5,572 for two qualifying children. If the child not going to school is under 19, then that would bring the limit to $6,269.

Click here for more information from TurboTax FAQ.