Other mistake: Nell's hair is considerably lighter in the scene where it starts moving by itself - clearly CGI.
Other mistake: As this is complicated you have to look for it very carefully. As Nell first enters Hill House she hears the sound of Mrs. Dudley that we later know comes from the kitchen. She follows the sound, going through a door on the right that leads to a long hallway. What is wrong here is that by the direction of the hallway, it should be passing right through the dining room. If not it should be passing beside it, which is not possible since we see that the dining room has tall windows to the outside. The other option is that the kitchen should be before the dining room, which is also impossible, since at dinner, Theo comes from the opposite direction and both Nell and Ms. Dudley come from the kitchen, through a door on the left side of the dining room, right beside the long stairs.
Answer: She has faith and the courage to face him without fear. After years of bring used and abused, she finally had enough. The only way to conquer your fears is to face them.