She didn't get along with her castmates and coworkers as well as the rest of the cast did. like dude said above, she in particular did not get along with Will Smith or Alfonso Ribeiro (they remember her as crazy, she remembers them as spoile and misbehaved young men).

Hubert breached her contract by getting pregnant during Season 3, but the showrunners managed to work said pregnancy into the plot and introduce a fourth Banks child to the cast. However, when it came time to do renewals for Season 4, given Hubert's breach of contract (and increased friction between her and everyone else while she was pregnant) the producers sought to "punish" her by reducing Hubert to semi-regular, docking both her overall pay and the number of episodes she'd appear in from 25 to 13. After a lot of back and forth, the producers fired her just before Hubert was about to accept their terms and went and recast Vivian Banks with Daphne Maxwell Reid.

Janet Hubert has been mad ever since.
https://www.youtube.com/watch?v=8_vuutzkyJY