Can one use a US passport with a valid ETA to enter Australia if Aus citizenship has been granted (but no Aus passport yet)?

Question

I applied for citizenship by descent for my daughter 4 months ago assuming there would be plenty of time to get an Australian passport before she travels to Australia at the end of July.

Due to a couple of issues that were not my fault the citizenship will only be approved this week, with no time to get a passport (she is already off on her travels in Thailand).

As a precaution i got her an ETA in her US passport before applying. I know the ETA would not be granted if she is already a citizen, but does anyone know if the existing ETA will be cancelled once she gets Australian citizenship?

I want her to enter on the US passport and get her Aus passport while she is in Australia. From what i understand the main problem is whether the airline will allow her to board.

Answer 1

So to update what transpired. I managed to contact the manager of the citizenship dept at the high commission in London, and she said that they can put off the final approval until after my daughter arrives in Australia with her US passport and ETA.

So immediately after she arrived in Aus, i asked them to finalize the citizenship, which they did the following work day.

After it was finalized, I checked the ETA website and they did not cancel the ETA for her US passport. So she would have been able to board the flight to Aus even after her citizenship went through.

Answer 2

The airline will allow her to board if they are satisfied that she meets the entry requirements. If the only travel document that she has on her is a US passport, then she will need to use that to fly to Australia.

The existing ETA will be enough to get her on the plane, and to be admitted to Australia. Indeed, an ETA would not be issued to an Australian citizen because it does not apply to them, however if no Australian travel document is in her possession and she's unable to obtain one before flying to Australia, she needs to make use of what she has.