Oooooooooh this is fun. And sort of! I am a simple guy who likes how some numbers/combinations look. She always gave me the vibe of a late summer/early autumn person so one day when I finally wanted to decide on her birthday I just wrote down dates that looked good to my brain. 8/30, 8/31, 9/02, 9/15, 9/16, 9/30. Something about them (and a couple others, a few in October for example) really scratched an itch. Eventually I settled on September 15th! It just felt right to me.