This should be straightforward and it would be were it not for the fact that your aunt has visitors parking in front of her garage too (it does make me wonder who's in the visitors parking if there are no spaces available).
But my approach would be to firstly ask the Executive Committee or strata manager to issue a warning to the 4WD owner – they are almost certainly in breach of by-laws.
Secondly, your aunt should ask the EC to monitor who is parking in the visitor spaces and, if need be, designate one of them for doctors, health professionals and other carers so that the people who really need the spaces can always find one.
If the EC issues a “Notice To Comply” to the rogue parker, they could face substantial fines from the CTTT if they continue to park illegally. Whether or not your aunt has a car is irrelevant.