Then again, the CE was quite afraid of starships and knew it was no match to their weapons and shields. If there only existed this single individual, as Marr seemed to think, then it could easily have been assigned a shepherd who kept it away from planets that had humanoid life. Starfleet surely would have had at least one ship to spare, a ship that could have kept on researching her chattel during the escort mission.
We never did learn what the CE ate. At Omicron Theta, it had killed the colonists despite their underground safe haven, without leaving corpses behind but also without damaging the real estate. It had not immediately destroyed/devoured the surface vegetation, either: the vegetation only died out after the Tripoli left, and was still in the process of dying when the Enterprise arrived a quarter of a century later. So did the CE return after the first starship had left, and had a bit of salad?
If so, we might decide it could eat vegetables, even if it also found people aboard unprotected spacecraft rather appetizing.
But the possibility remains that the CE eats souls, like any good scifi monster, and that the destruction of the vegetation is just a side effect - perhaps an expression of rage when the actual meal remains elusive? In that case, it would be quite a bit more difficult to give the CE UFP citizenship.
Timo Saloniemi