I’ve just come to the realisation that Hermione Granger probably memory charmed her parents and packed them off to Australia long before she told Harry and Ron she’d done it at the beginning of Deathly Hallows.
She literally never goes home from Goblet of Fire onwards, spending her summers with the boys instead. In GoF she’s remarkably blase about her teeth, something her dentist parents would have noticed and felt hurt about.
If I were to guess, I’d say she probably did it after the wizarding world cup when she’d seen exactly how the wizarding world treats muggles and decided not to let that happen to her folks. Hermione knows which way the wind is blowing and gets in early. She’d be more than capable of doing it.