Ok, if she's come off the track, and hasn't had a great deal of education, at this stage you really only need to be concentrating on getting her coming immediately off the aids - go, stop and turn.
If you are not overly sure on your basic dressage work, I would strongly suggest finding yourself a coach that can help you if you are looking into improving your flatwork.
Collection is the last stage of training of the dressage horse - your horse will not be working in collection for many years yet, at this point in time you need to be building up her strength and fitness to be able to sustain slightly more weight over her hindquarters.
It is much more difficult than it seems, to teach a horse to start working off its quarters and into the bridle, and takes a fair amount of knowledge and skill as a rider to do so - hence the recommendation that you look for an instructor. And being in Brisbane, you have multitudes of fabulous dressage instructors available to you!