Eunice is a new student that Hayley meets at Groff Community College in "The Sinister Fate!!".
Hayley is originally repulsed when she meets Eunice, but she soon finds out she's quite fun to be around. When telling the family about Eunice, Francine is similarly repulsed, but Hayley hopes that she can be just like her. Klaus points out that she's already destined to become just like Francine instead, pointing out their similar habits. Hayley tries to deny it, but the evidence keeps piling up but she quickly discovers that Jeff is even more like her mother. She sets out to de-program him, but his issues go even further than she imagined. While meeting with Eunice and her study group, she becomes even more impressed with the life Eunice has had. She learns that both Eunice and her husband, Milford, left home at an early age rather than become like their parents. Returning home, she finds Francine and Jeff engaged in a musical number, which is the final straw, as she grabs Jeff and takes him from the Smith home.
Together, they head to Eunice and Milford's home, where they are encouraged to change into their clothing to replace their rain-soaked outfits, unaware that Milford and Eunice have a secret plan to swap their brains into their younger bodies. To their frustration, Stan and Francine arrive to recover Jeff, but due to the pouring rain, find themselves also trapped in the house. Seeking out the bathroom, Stan finds their secret lab, but thinks it's just a man-cave. Tired of Francine and Hayley's bickering, Eunice, who reveals herself to be Constance von Stroheim, an escaped mad scientist along with her husband Wilhelm, commands their deformed handyman Morbo to capture the pair and take them to the lab, having decided to use their bodies instead and use Jeff for their cat, Mr. Poopy, while slipping Stan a pill to make him sleep. As Hayley apologizes while Constance is distracted by Morbo, Francine is able to remind her that they both share being double-jointed before the drugs knock her out. Hayley is able to use this to slip out from her shackles and knock Constance away from slicing into her mother's skull. Constance tries to send Morbo after Hayley, who reminds him of the beatings he's suffered at her hands. He instead turns on Constance and her husband, allowing the family to escape.
Enuice is voiced by Laraine Newman. Milford is voiced by Kevin Michael Richardson.