How am I supposed to know when/how friendship points are assigned or removed? I just followed the Developers walkthrough to a point where my "points" were zero - which is NOT a negative number. Therefore I should have been able to carry out a scene with her to gain a point. I couldn't. The results I got were the results the walkthrough said were for a negative score.
Does anyone know how they work?

Edit: There was a typo in the walkthrough. One option was with a score of zero, the other required greater than zero.