- “Uh, is this like a sex dungeon? I guess I should've been paying attention.”
The original Stacy presumably became a Cronenberg in Dimension C-137.
In "Rest and Ricklaxation", Morty was deprived of all his negativity, making him the ideal human being. He then went to Fancy Eats, where he hit on a single woman at the bar. Stacy initially showed no interest in him, since he was just a teenager, but was eventually won over by Morty's idyllic personality. They rode home in a limo, making out and developed a strong relationship on the way to Morty's house, most based on sex. Stacy talked about her fetish for Ben Wa technology and remarked on seeing Morty and his grandfather was arousing her. She also agreed upon the safe word "Sea Cucumber" with Morty. Obviously, the couple was planning on having sex when they got to Morty's place.
When they got back, however, Rick had invented a machine with the aid of Toxic Rick, which he planned on using to fuse himself and Morty back with their toxic selves. As they fought with each other. Stacy asked if it was weird she thought the fight was hot. Morty eventually begged her to get him out the machine saying their safe word "sea cucumber" in order to convince her that he was not okay with what was happening. As a result, Stacy forced open the door to the pod saying she'd do anything for Morty and managed to get him and Rick out at the cost of her being inside when it activated. As it turned out, it was actually a teleportation device, that would make her swap places with Toxic Rick and Toxic Morty, (originally planned as a trick for Rick and Morty, to get them trapped in the Detoxifyer). When Stacy got teleported there, she assumed it was a sex dungeon and went along with it.
Stacy remained in the tank, which was taken to one of the moon towers in town in the interim, for at least a good three weeks. She was only let out when a curious tour guide activated the tank, transporting her back into the real world screaming in agony "sea cucumber," scaring the tourists and causing the tour guide to fall off the platform.