She should have been aware that it is not allowed to bring fruit across the border. In fact, there are pretty strict rules about bringing in any kind of food items. She should have read the customs declaration form more carefully.
That said, the $500 fine is excessive. They should have just confiscated the apple.
I think the $ from fine goes towards paying for the assessment from the dept of agriculture. At least that is what is sounded like at the end of the article. They cant just throw fruit away just in case its diseased or carries pests, etc.
I believe the fine was for not declaring it. Customs asks if you have certain things and if you say no and then the item is found you are guilty of not declaring the item. If she had said she had an apple, they would have determined if it was legal to bring in and she would have had options if it was not.
She should have been aware that it is not allowed to bring fruit across the border.
https://www.heritage.org/crime-and-justice/report/ignorance-the-law-no-excuse-it-reality