I know that every day of waiting is excruciating. I have a feeling she will get her period and things will progress just fine. I don't think a delayed period is bad news or good news, even healthy young donors can have late cycles but still have normal hormone levels. If she is by chance a student, the semester-end crunch and exams in May (not sleeping and intense study) can be extremely stressful and cause a delay in cycles.
Are you on your second pack of active BCPs without a bleed, hoping to coordinate with the donor's AF?