I am not in NSW but the legislation where I am explicitly says a function of the committee is to supervise the treasurer. So, I expect the members of the SC can and should be monitoring the finances at least to the extent that they can satisfy themselves that the treasurer is doing things properly. I would expect that in practice some very trivial things could be left to the treasurer (eg. reimbursing someone for buying some light bulbs to fix a few common property lights) but other things should be committee decisions (eg. deciding to engage an electrician for more major work on the lights).
Also, the committee should be elected at each AGM. If the SC has not met for 18 months, am I right to suspect that perhaps you are not having AGMs either? If that is the case, then the OC is failing to comply with the legislation. Among other problems, there would be no approved annual budget to levy for and spend from.