Shall we look at even more facts? The woman was 79 years old. At that age your whole body is more susceptible to injuries. Even tap water that is only from the hot side with no cold water mixed in can burn elderly people. The cup of coffee wasn't spilled onto her because of something the employee did. It spilled on her because he was holding it between her legs so she could remove the lid to mix in the creamer. She was also wearing sweat pants at the time, which is known to absorb liquids. Because the coffee was hot, yes it would have felt uncomfortable no matter where it spilled on her. However because the pants absorbed the coffee, she wasn't able to get the coffee off of her fast enough so it was held there for a long period of time. You take anything that is hotter than your body temperature and hold it there for an extended period of time, eventually it will leave burn marks and possibly even serious ones. So given the situation, was it bad? Yes. Should it have been McDonald's fault for serving hot coffee? Not unless there was evidence that it was hot enough to scald the inside of your mouth when drinking it.
Maybe next time you should consider the whole story before stating that an argument was invalid.