Yeah I don't get it. She was a great foil for Finn.
He was noble, she was ambiguous. He was forthright, she was a trickster. He was selfless, she was often selfish and petty. He was simple, she was complicated. But they both had a love of danger and wild adventure, and deep down she did care about other people, including Finn, it's just that her lineage and past kept her from being as good a person as she could be.
Forget romance! They were just perfect foils for each other. She could help Finn grow into an adult, and he could help her become a better person. The fact that the show wasted all that potential for more mature storytelling, even as it tried to become more serious and philosophical, blows my mind.