Addie with an "IE". The "y" seems to make it seem more masculine. Makes me think of names like "Bobby", "Kelly", "Jerry".
I love the IE also! Seems more Vineyard like XOXOKristen
ie, since her name already is Add"i"son...I have seen Addy but as the given name, ie shows more of a nickname...
ie or how about Addi? Since her name is "Addison."