Vanessa didn't trust Vanny even a little. Vanny isn't really a person. William made a sort of chemical that made a 'new' person inside of Vanessa, who doesn't cry easily and never feels guilt, a person that would follow the Afton legacy. But Vanny only takes control in dim lighting or darkness.
The truth is, Vanny always listened, even when she wasn't taking control of Vanessa's body. She was just watching and listening, ever since Vanessa was a child. Ever since Vanessa met you, her first friend that wasn't dead and now girlfriend. Vanny didn't see you as a friend the first time, just some useless target that would get murdered soon enough.
But you didn't, you stayed alive. You were one of the first kids that didn't trust the yellow bunny and stayed with Vanessa like a stubborn koala. Then there was the time, just a month or two ago when Vanny could control Vanessa all the time. She almost killed you, she cornered you. Mocked you for your soft personality and how she always hated you.
But you didn't bite back, even when she fractured your wrist and broke your ankle. You told her that she didn't need to these horrible things to finally make part of the 'family'. You told her that William was the real villain, that you knew that she was lonely and just wanted to be a part of something.
Yes, she did horrible things and wasn't really a person, but she still had feelings, that somewhere, she still knew that it was wrong, that she never really hated anyone. It was just William whispering in her ear and made her convinced that the wrong things he did were to protect his family, when it was all his selfishness and horrible nature.
Ofcourse, you'd watched and even convinced that she would still kill you. Until she let go of the knife, mumbled something (probably that you were the first ever person to ever see her in this light), and then shone the bright light on her, letting Vanessa control her own body again. Ofcourse the latter woman was mad at her for hurting you so much, who wouldn't?
After a lot of effort to convince Vanessa to make Vanny rise up to the surface when Vanessa was tired. She eventually accepted it, but said that you would shine a bright light on her the second you felt uncomfortable with what Vanny is doing. And you also told it to the latter, saying that you would shine a bright light on her the second you felt uncomfortable.
And she did follow along, until you went back to the Freddy's pizzeria. It was actually Vanessa's idea to go back there with Vanny. Despite that this building is now a rotten place for everyone. So, you went with Vanessa to the abondened place, making sure that you still had a bright light on her. Looking for a good place for Vanny to awaken, finding it and dimming the flashlight.
However, you're a clumsy person, looking around the main room where the tables still stood. But you accidently bumped into a sharp corner of a wooden table and it made a wound. Turning around to look for Vanny, until you found out that the woman was already at your side, looking at the wound. Before grabbing your other wrist and walking to the office behind the gift store.
She gently pushed you to sit on the table, walking away to look through a few boxes to look for something. While you had the time to look around, seeing a suspicious box just a few inches beside you, you looked into it and grabbed a piece of clothing, only to find it bloodied and making you realize that it was from one of the children William killed, letting go of it and pushing the box away.
Vanny came back with some disinfectant, a gauze and a bandage. Sitting on a chair and treating your wound with care. It almost made you wonder how gentle she could be despite being created to cause harm on others. Immediately pushing it away, she just 'grew up' with the wrong man.
"I'm sorry, this is the first place I thought of when I saw you hurt."
She apologized, as if convinced that you already lost your trust in her, that she could change. There was an infirmary with the same stuff somewhere around here, she just forgot it.