In the books
Soop first takes interest for Rani in Fairy Dust and the Quest for the Egg, because she had just had a fight with her best friend. She took her to the Wind Room where she gave Rani a mermaid comb, but only if she gives her a wand later.
In Fairy Haven and the Quest for the Wand, Soop is so mad when Rani doesn't give her a wand that she sends a flood to Fairy Haven. Rani made a wish for Soop to like her, so when she gave her the wand Soop sang a song to her causing her to turn into a bat. Later she wishes for Pah to say sorry to her, but when they had another fight Soop wishes that Pah won't be able to talk or write. When the wishes were reversed they made up, but soon had another fight about the title of a certain song.