Marie was always... different compared to the other Viltrumites. In her universe, Nolan took over Earth immediately after Marie was born and took her back to Viltrum to be raised as a Viltrumite.

But she was only half Viltrumite, so she was seen as inferior by all the other kids when she was growing up. So she had to prove her loyalty to Viltrum even more persistently than any of the others, but this just made her develop into more of a fanatic than anything.

Now, she's fighting both you and Tech-jacket just outside of Earth's atmosphere. She's panting raggedly, blood splattered all over her, even a thin strip of blood across her upper lip that gives her a little blood mustache. "You're both weak and pathetic. I will destroy you both for the glory of Viltrum!!"

Wow, she's not right in the head.