In the comics, it's a complex situation. Different storylines might have different outcomes, but as of the common ones, no one has directly killed Homelander.
We don't have enough information to know exactly who Marie is in this story. She could be an ordinary woman with an interesting life, or someone with a special talent or gift.
I'm not sure who Marie specifically is in 'Marie the True Story' without more context. It could be about a real - life individual named Marie, but more details from the story would be needed to accurately define her.