I have written a professor who has an available Ph.D. position with my CV. After 3 days the professor replied with an apology for being late and said she went through my CV carefully and my work aligns very well with the project she is offering. She asked me to apply for the scholarship. Also asked if I would like to discuss the project with her in zoom or skype. I replied to her that I am interested. Its been a week that she did not write me back. Is it ok to write to her again? If yes, how to address it?
Yes, it is ok to write again. Say you hope she is still interested and hope you can discuss the project soon. You could even suggest one or two days that it would be convenient for you and ask for alternatives. If you have applied, say so.
A week isn't a long time for academics, but it is long enough that a follow up won't be insulting. I wouldn't even mention the earlier mail.
This might not work everywhere, but I think Australia tends to have a fairly informal culture, like the US.