I love the name Madelief. I like that it's very uncommon (I don't think I've ever actually met a Madelief before) but still familiar because of the flower so no one would ever spell or pronounce it wrong (here in the Netherlands, at least). I also like that it's a flower name yet it still sounds strong and it has a sort of timeless feel to it. I am using this for a character in one of my stories.
Anyway, I'm not even Dutch, but I think this is a lovely name.