The name "Vanny" is a mashup of "Vanessa" and "Bunny", which initially lead to speculation

In FNaF AR, the emails sent by Luis hint that Vanessa is troubled by something, as she looks up violent and dark things that isn't appropriate for the job at Fazbear Entertainment. In the last email sent by Luis, he asks Vanessa if she is "making a costume".

In the game files itself, the AI for Vanessa often calls back to Vanny on numerous occasions. The scrapped "Vanny Meter" is originally intended to impact Vanessa's AI. When filled, Vanessa will run off, which causes Vanny will take her place for the rest of the run. This only works in the scrapped Survival Mode, as a bug in the full game simply won't spawn Vanny even if Vanessa reached an end point in her path.

The tenth Retro CD that can be found in SB seemingly backs this theory. Vanessa was asked on the topic of making a costume, but she refuses to elaborate on what she made it for and why. This costume was also referenced in the scrapped AR emails by Luis, as he asked what the fabric material being sent in was for. This suggests that Vanny is a costume created by Vanessa herself, though it doesn't say if Vanessa wore the costume herself.

The Animatronic Encyclopedia fully confirmed this theory where the two characters are filed under the "Vanessa/Vanny" page. The book states that Vanessa created Vanny to carry out Glitchtrap's orders.

Both Vanessa and Vanny have two very different personalities. Vanessa is touted to be "helpful" where Vanny is psychotic and murderous. The Fire Escape ending was one of the points used for this theory. In it, when Gregory takes off Vanny's mask, Vanessa is seen. Thouigh in the post credits, Vanessa is seen on top of the roof, looking down as the pizzaplex continues to burn. This suggests that Vanessa and Vanny are two different people, or that the two are identical twins with two different personalities.

This theory is debunked in the Animatronic Encyclopedia, where Vanessa and Vanny are stated to be the same person. (See: Vanessa is Vanny).

In the unreleased AR emails, Vanessa's last name was stated to be "A.", which could stand for "Afton". As Vanessa is involved with Glitchtrap and Burntrap, this could be possible, but is not heavily supported outside of that.

However, there is one discovery that seems to joss that theory. In the security office where you control a Pizzabot, you can find a photo of two people wearing Glamrock Freddy masks that says "2035". This implies that either this is the year where SB's gameplay occurred, or that the Mega PizzaPlex was open around this time.

Vanessa in the emails is stated to be 23, meaning that she would be born in 2012 if you where to subtract that age from the time the photo was taken. William Afton died in 1993 after the FNaF 1 location closed down and wasn't found until thirty years later, which makes it impossible for Vanessa to be born at that time if she is the daughter of a serial killer.

This theory also seemed to be bunk because William Afton has not been mentioned in Ruin or the Pizzaplex books.

In the Retro CD's, Vanessa was being questioned about her time during the events of FNaF AR. The speaker notes that someone was looking into Vanessa's personal files and knows a lot about her. Vanessa denies the existence of this person.

In the CD's where Patient 46 is questioned, the speaker talks about how they are a skilled hacker and where the reason why the Pizzaplex robots were malfunctioning. According to the CD, what 46 did is that they took the glitch and subtlety hid it before unleashing it.

These actions from Patient 46 lines up with the events in the AR emails. In them, Vanessa tricked the workers at the Funtime Delivery Service to give her access to the company credentials (special permission to access vital data), which led to her putting Glitchtrap back together, hiding him in a plush, then having it be unleashed. It's not clear if Patient 46 took over the rest after that.

With the Tales of the Pizzaplex story "GGY" revealing that Gregory is Patient 46, it means that the two were indeed connected. Bizarrely, neither Gregory or Vanessa recognize each other despite the limited encounters. It's not clear why the two didn't know each other. While Gregory could be lying that he doesn't know who Vanessa is, it doesn't explain why Vanessa didn't recognize Gregory during the events of the game. It could be possible that either they're both lying to cover each other up, or their memories were somehow wiped by Glitchtrap.

This seems to be further backed in Ruin with Vanessa and Gregory going back down to the Pizzaplex to seal The Mimic away to prevent it from corrupting both her and Gregory again.

The Animatronic Encyclopedia debunks a part of this theory where Vanessa is listed as a "human" instead of "animatronic human". While the Elizabeth part is still left uncertain, neither page involving Vanessa or Elizabeth mentions the theory of the two being connected in some way.

This theory also seemed to be bunk because William Afton has not been mentioned in Ruin or the Pizzaplex books.