IANAL

Her insurance will not cover a claim that predates coverage. However, part of the financial review process that the financial assistance department might need to approve her for waiver might require an official insurance denial of coverage. If she was treated in September and applied in October and is now being reviewed, she would have active insurance during the review claim period. The job of the aid department is to validate through data the necessity of each person’s case, so The official review process may need an official notice of rejection of coverage.

Or, the insurance carrier may reject the bill but establish a new maximum billable reported amount based on the insurance policy coverage. So 20k may be renegotiated to 14k, and you may be able to take that back for a waiver, or take the denial letter back and add it to her current application. That would reduce the official amount they were forced to write off in documented waivers.

She won’t be approved for coverage to my understanding, but she may have a second chance at being eligible for a waIver when armed with the denial.