The way I look at it is like this.
1) Let's just assume the Oracle can predict the future. Maybe it's because she can read the code and apply your statistics to a given situation or because she loads the program related to a certain time in the Matrix and then watches your reaction. Either way, it gives her a vision of the "future".
2) None of this affects your "Choice". Just because the Oracle sees you taking a drink doesn't mean you are forced to do it. Instead, you have choice to order the drink or not. The Oracle can only see the choices that you make.