I sometimes don't mind nns when they are just a simple shortening of a longer name (
Joe for
Joseph) but usually prefer the full name. I would be in the same camp as your friend - if you are going to call her
Ann, then just name her
Ann (although please spell it
Anne).
I much prefer the full name
Malcom to Mac. On the flip side, I don't like
Cornelius, but if you are going to call him
Neil or
Conor, then just name him
Neil or
Conor.