There are two processes by which a committee member can be removed from office in NSW; a special resolution at a general meeting and by orders from NCAT.
However, that is jumping the gun. In your shoes I would be presenting the owner with a series of requests giving her the chance to put things right. These would be:
1. A request for a full inspection of the changes by a certified surveyor, at her expense.
2. Her agreement to all the by-laws necessary to protect the owners corp against claims if any of the renovations prove to be faulty or have an impact on common property.
3. Retrospective approval from the local council planning department for changes she has made and remediation where that wasn’t forthcoming.
If she was not prepared to accept any of these conditions, I would quietly explain that the next step would be a general meeting specifically to have her removed from the committee (where all her actions could be aired publicly) followed by action at NCAT and through the local council to have all the unauthorised changes restored.