Dib and Zita are classmates at Skool. Out of all the classmates, excluding Zim, Dib interacts with Zita the most, and it is generally shown that the two have a mutual dislike for each other, as Zita constantly belittles Dib for his interest in the paranormal while Dib gets annoyed at Zita (along with the rest of their class) for not believing him about Zim being an alien.
In "The Nightmare Begins", after Dib makes his accusations about Zim being an alien, Zita was the first one to doubt this claim, stating "Oh, not this again. You're crazy". Later on, after Dib is close to exposing Zim until the latter also agrees Dib is crazy, Zita states that it makes a lot more sense.
In "The Wettening", Zita is among the crowd who watches Dib during his attempt to splash Zim with a water machine. Specifically, she can be seen standing next to Gaz. She immediately runs when she sees the huge water balloon from Zim's orbital launcher.
In "Bad, Bad Rubber Piggy", when Dib is trying out the headset he got after Zim messes with the past, he says that he is going to spy on the "family of nosferatus" that just moved in. While not confirmed, most fans have speculated that the "nosferatus'" were actually Zita's family who moved in, which could explain why Zita hates Dib so much. Later, it was shown that she had known Dib since they were kids, as a younger version of herself is seen watching Dib being treated by the medics.
In "A Room with a Moose", Dib attempts to convince the class about Zim's plan, only for Zita and the others to shoot it down by calling him crazy. In the episode's climax, he shifts himself to the other side of the bus, the side where the kids sit, which causes all the kids, including Zita, to shift to the other side to get away from him, shifting the bus's weight to the left and causing the bus to go through the portal to home.
In "Bolognius Maximus", Zita was the first one to point out the horrible smell coming from Dib, and cheers when he is kicked out of class.
In "Halloween Spectacular of Spooky Doom", Zita initiates talk about how Dib seems "more crazy than usual" and states how Dib has "a long history of crazy", further implying that the two have known each other for long. She also states how Dib is always screaming like a "howler monkey" and, after agreeing with the other classmates, asks Ms. Bitters if she could use a crazy card to send him to the Crazy House For Boys. After Ms. Bitters asks her if she's sure that she wants to, Zita looks at Dib acting crazy one last time before confirming that she is sure. However, her actions leave an opening for the Halloweenies to kidnap Dib.
In "Mysterious Mysteries", Zita was one of the three kids who were interviewed about Dib's sanity, to which she replies "He's pretty crazy".
In "Lice", after Dib finishes his presentation about Galileo, Zita immediately called him crazy, which earned her an A.
In "Vindicated", after Dib knocks off Zim's fake eye, Zim claims that he is only suffering "pink eye", with Zita agreeing with his statement, stating how Pinky has it pretty bad.
In "The Frycook What Came from All That Space", after Dib accidentally insults Pigboy, Zita angrily warns him to watch what he says around the latter.
In "Gaz, Taster of Pork", when Gaz throws some mash potatoes at Zita, hitting her in the eye, Dib strangely shows concern.