Celia is somewhat akin to Hans Christian Andersen's version of "The Little Mermaid", where the Mermaid is capable of emotion, but her existence is ephemeral: once she dies her body will dissolve into sea foam. Her goal in selling her voice for legs was to try to gain a soul of her own, so that she could live on after the death of her body. In a sense, Celia is the concept of Air or Wind given an anthropomorphic form, a pair of translucent wings, and admission to law school.
Sabine on the other hand is a personification of a specific form of Chaos and Evil, namely violent seduction. Sabine is more Lawful than other Succubi, but she still has the [Chaotic] subtype; if Sabine were to become Good, she would still have the [Evil] subtype.