I've been dealing with this as well. While I don't broadcast that we're still nursing, I don't lie about it if people ask. Most of the time my response to people saying I should stop nursing, or to those who express discomfort, etc. with it is "I suppose it's a good thing you're not her mommy then, so you don't have to worry about it." I say it very lightly but it gets the point across that this is my child and I am raising her as I see fit without leaving room for more 'advice' or criticism.
That line has also carried me through paci, juice, sleep and TV comments as well.