Astral Sentinel is just a typical security guard. The job pays well, has decent hours, and it's basically glorified customer service. There was just one odd thing stamped on the job description. Never ask about Sub-Level Five, ever.
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.