The fact that she receives this nontaxable income would not prevent you from claiming her, but you would have to be providing more than half her support. This income is not listed as one of the income sources that is left out of the support calculation. That means you would include this amount as income she provides for her own support, even though it's not counted in the income test
I'm including here the link to an iRS worksheet designed to help you determine whether she qualifies as your dependent considering support she provides for herself and that you provide for her.
There are other qualifications for your ability to claim her, and the second link provides a very readable explanation for Qualifying Relative Dependents.
https://apps.irs.gov/app/vita/content/globalmedia/teacher/worksheet_for_determining_support_4012.pdf
https://apps.irs.gov/app/vita/content/globalmedia/4491_dependency_exemptions.pdf starting on p.7-6. Note that this income source does not count as part of her total income.
