Excuse me? I just spotted this the second time I read the article. Is she an illegal?
No, she's not. Illegals actually wouldn't care what the immigration officials thought of them and whether or not they had committed any crimes. It's just that a conviction of any sort will give immigration an excuse to deny you a visa on your next visit, even a tourist visa. John Lennon most famously was denied an entrance visa to the U.S. because of a marijuana conviction in the U.K. He later fought it and won I believe. He then refused to leave the U.S. for fear that they would deny him entrance again.
No, she's not.
But one thing that is typically stressed on travel advice issued by the Australian government for Australian citizens going overseas is that fact that local laws should be respected (should be obvious, but Australia has just as many obnoxious idiots as any other country) and the consequences of breaking those laws. One of these in many countries including the US is that a conviction may well prevent you being allowed to return to that country. For a person who is intending to travel to the US again at some point, this is a valid reason for concern.