Congrats again!
If I couldn't use
Maggie (which I used to dislike but is growing on me), then I'd use
Maisie or
Meg /Meggie.
I like
Maisie best, although I tend to think of it as a name in its own right.
I seriously could not imagine anyone using
Madge. Very unattracive in my opinion! The others are ok, not my style though.
I've seen the name pronounced Mar-ghee spelt as Margi but it's a bit ambigious.
I will spare you my feelings on
Gretchen in case you do decide to use it, but in a nutshell, I don't really like it. :-)