One of the disqualifiers that is not so obvious is having taken a prior year distribution.
The amount of any contribution eligible for the saver’s credit is reduced by the amount of any taxable distribution received by the taxpayer (or by the taxpayer’s spouse if the taxpayer filed jointly with that spouse both for the year during which a distribution was made and the year for which the credit is taken) from any plan described in A-5 below during the testing period. The testing period consists of the year for which the credit is claimed, the period after the end of that year and before the due date (with extensions) for filing the taxpayer's return for that year, and the two taxable years that precede the year for which the credit is claimed.
One thing that is common overlooked is that this is a nonrefundable credit, meaning that it cannot be used to reduce tax liability below zero. Perhaps your daughter's income tax liability on Form 1040 line 18 minus line 19 is already zero without this credit. This credit cannot be used to reduce other taxes such as self-employment tax and early-distribution penalties.