I think I figured it out - she no longer qualifies as a fully vaccinated traveller so has to provide a pre-entry test for admission. We don't have a PCR while she was sick because we were isolating, and being symptom free we are 10 days or so from being able to re-qualify as a fully vaccinated. In the mean time, the choices are lie on the screener, or wait 10 days or hope for a negative test.
Of note, 10 days where we are will cost more than the fine - the incentive here to lie is very high, hence likely why we import so much covid. Integrity sucks.