"Mae hi'n dod o Awstralia yn wreiddiol."
Translation:She comes from Australia originally.
That would be 'O awstralia mae hi?' Which is a different kind of sentence in Welsh, an emphatic one, which comes up later on in the course.
The sentence above is the simplest way of saying where someone comes from.
I think what Captanne is asking is why "She comes from Australia originally" is correct but "She is from Australia originally" is wrong. In English those are exactly equivalent as far as I can see. The question mark may have confused you, it's not part of the example sentence.
I agree with Nespera, I put She's from Australia originally, and it was marked wrong. I've reported it, as 'She's from...' is a natural way of saying that.
I mentioned "She originally comes from Australia" and was marked wrong, with the correct translation mentioned as "She is from Australia originally". What was wrong with my answer?