I can understand why the spelling seeming more usual to you, because it is your cousins name. I always gave people funny looks when their name was
Robin, as my cousin is Robbyn. But anyway, I think there are enough "funny spellings" of
Caitlin:
Katelyn,
Kaitlin, Caytlin, etc. without getting everyone confused. I wouldn't mind Caitlan in the mn spot to honour your cousin, but
Caitlin is overused enough as it is without its many spelling variations.