I'm not a big fan of
Cadence in the first place, but I'd much rather see that than Kaedence or Kaidence. Neither spelling is out of the realms of possibility (I've seen both before), but they are kreaytif enough that I wouldn't smile if I saw them in the
BAs.
If you want to call her
Kaede, do so. Nicknames don't have to be spelled like the name itself; I love
Cassandra nn
Kassy.
Cadence nn
Kaede is a far sight better than Kaedence nn
Kaede, IMO--because
Cadence is more than just a name. It's a word. And if you're going to use a name that's also a word, it looks plain ignorant to misspell it.
And unless you have weird family naming dynamics, I don't see why it'd be too close to
Kay, particularly if you don't think you'll be anywhere near her.
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