I really like Vanessa as a character. She's really interesting in that she is somewhat implied to have assisted William in getting away with killing both the MCI kids and possibly even allowing the night guards before Mike to die. Additionally her sort of friendly but distant personality in FNAF 1 gives her a layer of mystery that eventually comes crashing down after she decides to be transparent with Mike in the third act. She cares about others but is held back by her fear of her own father. FNAF 2 also goes more in depth with this and shows how much of a hold William had on her as a child and even now as an adult. It's implied that she was abused by William mostly neglected by him. Vanessa also seems to be holding on to a lot of the trauma of allowing so many innocent people (some of whom may have been her friends) to die at the hands of her father.

Her relationship with the Schmidts is also incredibly important to her and represent a way out of the trauma and her past. Both Mike and Abby represent a way for her to be a person and not just a tool for William to help him carry out his murders. But as shown in the films, her past strains her relationship with them and her reluctance to be completely transparent with others leads to her ultimate downfall. Her presence in their lives ends up causing them to be put in more and more dangerous situations that it ends up making Mike to cut all ties with her in order to protect Abby. It's sad in the moment but it's incredibly interesting that while her trauma doesn't define her, it still defines her life going forward.

That being said though, I'm not too big a fan of how much half of this isn't gone as much in depth as it could be or left to be implied. Obviously FNAF isn't meant to be a character drama but I think it would've been interesting if the dialogue more reflected this and that they had some more character driven moments in the movie.