If you like Maddie, call her Maddie!
I honestly don't get these in depth analyses of what a nickname will be, when the point of them is that they evolve, they aren't designated.
If you want her to be called Maddie everyday, call her that.
If not, she'll end up being called Grotty or Angel or Binbag or something totally unrelated to her name, but which is a loving memory or familial in-joke and which means so much more than some pre-determined "official nickname"