Donna
We just love that the name this person used had to be Donna. Usually, Donna is a woman who works as a secretary at an office, we do not mean to fall into a stereotype, we are sure strong and independent Donna exists. But the name just reminds us of women we see in old television sitcoms.
Anyways, it would appear that Donna was pushing the thermostat to its highest measure and cooking everyone instead of the office. Maybe that was her plan all along and she just had enough of everyone. She wanted to get revenge for the way they had been treating her and the thermostat was the best option she had.