This is known as a red herring fallacy, the fact that it fused her labia doesn't change the nature of the situation, nor does it increase the gravity of the situation.

"She placed the coffee cup between her knees and pulled the far side of the lid toward her to remove it. In the process, she spilled the entire cup of coffee on her lap. Liebeck was wearing cotton sweatpants, which absorbed the coffee and held it against her skin, scalding her thighs, buttocks and groin."

Additionanally:

"According to a 2007 report, McDonald's had not reduced the temperature of its coffee, serving it at 176–194 °F (80–90 °C), relying on more sternly worded warnings on cups made of rigid foam to avoid future injury and liability (though it continues to face lawsuits over hot coffee). However, in 2013 the New York Times reported that it had lowered its service temperature to 170–180 °F (77–82 °C). The Specialty Coffee Association of America supports improved packaging methods rather than lowering the temperature at which coffee is served. The association has successfully aided the defense of subsequent coffee burn cases. Similarly, as of 2004, Starbucks sells coffee at 175–185 °F (79–85 °C), and the executive director of the Specialty Coffee Association of America reported that the standard serving temperature is 160–185 °F (71–85 °C)."

So not only did it not change the temperature at which most major brands serve coffee, the temperature that was proposed as reasonable by the defense attorneys was also still hot enough to cause third degree burns. I get that she might want them to pay for damages, but she literally dumped it on herself, the reason she was so seriously hurt was because she was 79 years old. If you're buying hot coffee that's freshly brewed then it should be obvious it's hot enough to seriously burn you. If it's over 150 F then you will get major significant burns.

As to the idea that they had been warned:

"Other documents obtained from McDonald's showed that from 1982 to 1992 the company had received more than 700 reports of people burned by McDonald's coffee to varying degrees of severity, and had settled claims arising from scalding injuries for more than $500,000."

McDonalds purportedly sells more than 50 million cups of coffee per year, over 10 years that was 500 million cups of coffee. 0.00014% is hardly a "warning."