This is actually perfectly normal, anonymous. You see, the “glow” you observe whenever a psychic-type uses its abilities is actually psychic “run-off,” so to speak; it’s just their aura flaring up after being charged with psychic energy from the exertion of using their own powers. This is also why the more powerful the move, the brighter and more massive the psychic aura.
However, if a psychic-type exercises their abilities regularly, they can actually diminish their auras until they’re barely noticeable. It’s very much like getting used to a certain level of activity as you physically get into shape. In fact, many psychic trainers aim for this phenomenon precisely because it not only means their pokémon have mastered their abilities but also allows them to become far stealthier on the battlefield.
In your espeon’s case, though, it sounds like she’s exercised her levitation abilities so much that it’s practically second nature to her, and thus, her psychic energies are far more focused on the task, leaving very little stray energy to charge her aura. You may notice her aura returning for other moves, but if it doesn’t, you shouldn’t worry, either. Considering the fact that levitation isn’t a natural ability for espeon, it’s likely yours has mastered the abilities that are.
Still, keep an eye out for any sign of psychic overexertion, including bloodshot eyes, a bloody nose, lethargy, a lack of appetite, or a sudden, explosive reappearance of her aura. If she’s constantly exercising her ability, this may be a possibility (as rare as it can be), and if any of this occurs, you’ll need to get her to a pokémon center as soon as possible.