Mildura is my home town (born and bred and lived there 40 years, most of my family still do), but lately the tone of the once-quiet country town has changed for the worst. There is an epidemic of ice addiction, with all the associated problems. Not saying directly that this has anything to do with this terrible crime, but just giving some background as to the undercurrent ripping through the area. Addiction to this relatively cheap high seems particularly prevalent in the lower socio-economic groups there - My opinion only.
Curious as to why you'd connect this with the Wynarka little girl, Puggle? The Karoonda highway is a fairly common route from Mildura to Adelaide, but less so since the entry into Adelaide via the Sturt highway has been upgraded. I've travelled that way many times, but not this year. (Pro tip: The little cafe/shop does an excellent steak sanga - and this is NOT my opinion only - family love it too!)