I can't buy your argument because of the unknowns (even though you get props for finding the temps at which skin burns and how long it takes at each temperature).

Why? Because I haven't seen the time elapsed from when it was poured to when she spilled it on herself.

Your premise is that it was 190 degrees at that point. That's something that is unknown because she was a passenger, they had already received the coffee, paid for the coffee, driven out of the lot and then pulled over somewhere for her to add cream and sugar. Now it may have been 190 or it may have been less.

You also state that if it were a less-hot temperature, she would have had more time to get the scalding liquid off of her.

However, now much time did it take her in this instance? She's a feeble old woman, what if she DID spend 20 seconds trying to get it off of her skin and clothes? We don't know that. I mean if it DID take her 20 seconds, then the coffee could have been at that less-than-190 serving temperature that is suggested coffee be served at to be reasonably safe, right?

So how much time did it take her to get up, out of the car, and stand up and shake off the coffee? 2 seconds? 1 minute?