The student loan interest is an adjustment to income and lowers the taxable income it does not qualify for a credit. Your daughter had only an income of $9,000 and the standard deduction of $12,000 (for a single filer) reduced her taxable income already to $0. Therefore it didn't help her to claim the student loan interest.
Please see this FAQ for more information on student loan interest deduction:
https://ttlc.intuit.com/replies/3302319
