It is impossible to predict their moves, so don't even try....
Maybe next time you shouldn't say that you need to know so that you can make other plans because she will think she is dictating the pace and controlling your Agenda. Because it could look like are making her a priority and obviously are just waiting around for her invitation. I think you could say, let me think about it and call me in the morning. That way she has to make the call to find out what's going on.
