There's nothing to say she absolutely must be one of the preexisting types, I suppose. Bella could be a Tinkerfairy Pony, who flys within a globe of colored light that happens to hold in an atmosphere, and which forms fluttering brighter bands that look from a distance like a hummingbird's blurring wings, for instance.
Perhaps it forms when she jingles the bell on her necklace?
--
"Anko, what you do in your free time is your own choice. Use it wisely. And if you do not use it wisely, make sure you thoroughly enjoy whatever unwise thing you are doing." - HymnOfRagnorok as Orochimaru at SpaceBattles
woot Med. Eng., verb, 1st & 3rd pers. prsnt. sg. know, knows
Perhaps it forms when she jingles the bell on her necklace?
--
"Anko, what you do in your free time is your own choice. Use it wisely. And if you do not use it wisely, make sure you thoroughly enjoy whatever unwise thing you are doing." - HymnOfRagnorok as Orochimaru at SpaceBattles
woot Med. Eng., verb, 1st & 3rd pers. prsnt. sg. know, knows