Georgi,
I think the closest Ronald McDonald house is the one that FlowerChild is talking about, Garrick Terrace right behind the Royal Women's Hospital.(in Herston) It would only be a 10min drive from Mater in reasonably good traffic flow.

If it helps, here is there number to save you looking it up 07 3257 0328.
to find out how it all works here is the website for you as a quick link
Ronald McDonald House - Herston

you're doing so great Georgi. xx