All clerks have a job description and should have an annual appraisal, carried out by two or more councillors. This provides a regular opportunity to consider the clerk's performance against the specified requirements of her role. Where shortcomings are identified, an action plan can be agreed to address them.
If the clerk has awarded herself a pay rise that was not agreed by the council or included in her contract of employment, this would be a disciplinary matter. Some employment contracts offer automatic progression up the pay scale, so if this is the case, she may have done nothing wrong.
From the information you have provided, it sounds as though the tail is wagging the dog and, if this is the case, there will be difficult conversations to be had if you are to turn things around. Whatever feelings of anger or resentment you may harbour, do not lose sight of the fact that the employer has a duty of care to the employee.