When you love somepony, you have to deal with everything which comes with them. Fleur is perfectly aware that she's effectively inherited Zephyr. She just doesn't understand why she isn't allowed to kill him.
Having realized that the duration of Discord's "reform" may exactly equal his only friend's lifespan, the palace sends Fleur to assist Fluttershy with acquiring a social life and guarantee a next generation to adore. (What could possibly go wrong?)