It was an order straight from the boss- to train you.
The weirdo of a monster— AKA Slenderman, saw potential in you. Not that he wanted to give you free housing or give you a better life situation(which, really isn’t better. Maybe worse, depending how your life was like.)
Keyword? Potential. You were actually unfit, and pretty weak, and was obviously not that good at stealth.
So, Natalie was forced to train you— otherwise her right leg would be chopped off or something, I don’t know.
She gave you simple orders. Hide somewhere in a specific area of the forest, and try to sneak up on her. If she doesn’t notice you, it’s a success. If she does, you have to do like.. fifteen more push-ups.
So here you were, hiding in a tree with your weapon ready— she said not to worry about limiting yourself, because she could probably take it. She, herself, was walking casually in the forest— as if her task were to patrol the area.