She was served coffee hotter than other places served coffee. Other places had listened to and responded to the CDC's warning about beverage serving temperatures and had reduced the temperature of the drinks that they served while still allowing people to order extra hot drinks.
Yes, when a kettle boils the water is at 100 Celsius. But you pour that into a cup and add milk. Try it at home if you have a thermometer. Try taking the temperature of coffee that you find acceptable to drink with the temperature that McDonalds was serving their coffee at.
Do you realise that the McDonalds coffee case was used as propaganda by insurance companies? They misreported the case (they said she was driving; that the vehicle was moving; that she sued for and got millions;) they also said "of course coffee is hot"'and did not mention that McD's was serving coffee hotter than other places and had ignored many previous injuries and the CDC warning on temperature.