S.
I really don't have any great advice for you, it just made me laugh! My daughter (who is now 2.5) would not drink from a sippy cup at all. The only thing she would drink from was a cup with a straw. I have no idea how she learned this, just one day she started drinking it. I think going from sucking on the bottle straight to sucking up on the straw was big. I wish I knew how so that I could give you some decent advice.