You did the right thing in my opinion. Just b/c you told the server or restaurant that you were only going to have drinks doesn't absolve you of the obligation to be a reasonable tipper, especially when you sat for quite a while and she brought you snacks. It's one thing if I order a six dollar glass of wine at the bar and stay for ten minutes to push a dollar over; it's another if I stay for a while and the bartender is pretty attentive and brings more drinks and snacks.