Did you ever stated your criteria for the Bells somewhere?
Most Bells get flying animals. The ones that don't (e.g. Juliet's tiger, Aether's pangolin, Sarion's raccoon) are associated with a sort of... knocked-around quality, although it's not just who I've been meanest to, it's a particular emotional tone associated with it that those three have which e.g. Shell Bell doesn't have. There's also a shared quality between the two with kinds of flying squirrel (Glass, Aegis) which I haven't tried to articulate before... both of them grew up in environments that were nurturing without being quite open-ended. Izzy and Ara get bats but except for the fact that I wanted them to correspond and that's why they
both have bats I can't explain why bats.
The Bells in worlds with funky animals (Ace, Chi) will get funky animal daemons (Altaria for Ace, "riverbat" is a bat/otter cross for Chi). T'Mir will have a Vulcan animal but I haven't decided on its details yet (though I named it independent of that; whatever it winds up looking like it will be called a kes'lat). When we do Mira, her world has winged mice in it and she'll have one for a daemon.
The bug Bells have nothing special in common: I wanted to give Rose a stinging animal since she has the mental defense that bites back so she got an attractive sort of bee, and Pat is being Default Modal Bell so she got one of the things Path found appealing for Bell reasons rather than for Amariah reasons (the glowing is a luminosity thing). Butterfly will get a butterfly (a Hewitson's forester) mostly for thematic reasons and because she's intensely vulnerable on a personal level.
The three with dragons (Stella's red, Golden's gold, and Tab's not-so-mini white) are linked to the fact that their worlds are related (ingotry, witchcraft, Gifts).
The rest of them have birds or I haven't decided what they have yet. These are
mostly chosen for aesthetics - the sort of thing that would look right with the character. Although I remember picking a smew for Shell Bell in particular because the pattern of markings on the males is described as "broken" (and I wanted an aquatic harmless bird), Phoenix gets a phoenix, Clarity will also get a phoenix but it'll be a constellation (we've decided that there are more constellation critters than just ursas in Equestria), Etty gets a swan, and Lailah will get a greater honeyguide, all of which are for reasons.
Note that with the exception of Amariah's Pathalan, Cam's Grace, and Shell Bell's Neptune, none of the daemons are actually instantiated at this time so when I say "have" I mean "would if they went unprotected to Alethia".