And apparently you don't intend to. You think like the government if you support mandatory tipping. I am not going to defend these particular actions by this woman. I am only expressing my disagreement with the mandatory tipping policy in general.
Since the article indicates that they frequented this establishment making it seem that she would know the tipping policy beforehand then she was obligated to pay up regardless of the service. But it makes you ask "Why the stiff this time?" The answer would probably land squarely on the back of the waitress. The "pastor?" didn't stiff the restaurant she stiffed the waitress. Why, we don't know but your assumption that it was because of the cook or something else with the restaurant is not logical. The article only says "... a disagreement over the establishment's auto-gratuity of 18% for parties of 8 or more...". She had to know of the policy so why the dispute on this particular occasion?
You yourself said "A tip is not about the restaurant's service, it's about the waitresses service to you." Why don't you understand what you are saying? The rest of your argument is about hourly pay that is contracted between the employer and employee and not applicable to this conversation.