In "Rest and Ricklaxation", Morty was deprived of all his negativity by an alien spa, turning him into the ideal human being. Rick tried to inject him with his negativity again, but Morty escaped on a jet pack and moved to New York, where he worked as a stockbroker, bought a high-class apartment, and landed a gorgeous redhead, known as Jacqueline.
Jacqueline lived in Morty's apartment and had a perfect relationship with him. She also worked a job of her own as a public fundraiser speaker for bio-tech related businesses. She felt remorse that one of her fundraisers was going to cut into her time for dating Morty, so she cancelled just to be with him.
When Jessica made a phone call to Morty, he failed to hang up, making the call over a minute long, allowing Rick to trace his location and find him. He invaded Morty's home, injected him with the negativity, and turned him back to normal again.
Morty had to break it off with Jacqueline. While he did, Jacqueline explained how he managed to win her over with not only being the model of a perfect man, but also because of his unending honesty and she considered him to be a soul mate. When Morty gave up his life with her, he left her with ownership of the apartment, where she apparently still currently resides.
Not much is shown of Jacqueline's personality in her short appearance other than that she cares very deeply for Morty. She never has any conflict with him, and doesn't even have a shred of unironic jealousy over him calling his ex-girlfriend. She considers Morty her soulmate and sees him as the best thing that's ever happened to her, since he dispenses happiness, fun, comfort, wisdom, wealth, shelter, security, and love for her. Strangely enough, she managed to take him leaving her very well, suggesting the reason the two were so good for each other was because they were so open.