Silence does not mean consent or approval. Approval is an active process which has to be commenced by the person seeking approval actually asking for it. If it were otherwise, anyone living in a strata scheme could do what they like and then wait to see whether the OC objects.
Presuming this is in NSW and the balcony is common property, the works would have been undertaken when the old Act was in force, but the new Act provides at section 111 that an owner of a lot must not carry out work on common property unless they are authorised to do so.
It is not uncommon for owners to carry out works and/or install things that affect common property without approval, either by accident or design. In respect of anything that is on common property, or effectively then forms part of the common property, it is then the property of the OC, and in the absence of an exclusive use by-law the OC is responsible for it. The other element of this is that the OC can then determine to remove anything that is on or forms part of the common property.
For example, the previous owner of my apartment installed a range hood which was ducted into the ceiling. As no approval was given for that installation, and no exclusive use by-law was put in place, the part of the installation that was in the common property was the responsibility of the OC, and they could have removed that ducting at any time.
I am not sure why your friend is so worried, and after 7 or 8 years it seems a bit silly that she is not using something that is causing her so much concern. I suggest the best course of action is to lodge an application with the OC seeking retrospective approval so she can get on with her life. If no-one has raised concerns to date it is highly likely she will get approval and she will have clarity about the issue going forward.