Ms. Bitters is the Skool teacher of Dib, and the two have a cold relationship. While Dib is regularly annoyed with his teacher for her harsh treatment of him and the other children, Ms. Bitters views him as mentally unstable, and is quick to reprimand and punish him at the slightest provocation.
Ms. Bitters sees Dib as 'crazy', despite him being the most normal child in Skool, and likely among the brightest, as he is the only one to notice that Zim is obviously an alien.
In one episode, she allowed Zita to use a Crazy Card to send Dib to the Crazy House For Boys. She is constantly annoyed by Dib's and Zim's various shenanigans, but believes the latter to be merely a regular student; whenever their conflicts in Skool result in disaster, she tends to blame Dib for the damage. She also sees Dib as being very annoying, having stated on one occasion that he "squawks like a fruit bat."