First, willpower is reset to the maximum (before modifiers like from the Womb of Lust curse) each day, so feeding her potions/Sweet Memories to drop willpower only works for that day.
Second, willpower doesn't need to be 0 to get a "pink" scene, except maybe at the very start of the game. Current Lewdness and some other factors (sensitivities, fetishes, Perversion passive traits like "But it's so Cute!") can bring effective willpower down. So e.g. you have 20 willpower when you go to start a boobs-flashing scene; 10 lewdness, 5 exhibitionism and 5 breast sensitivity would bring effective willpower down to 0 and allow you to do the "pink" version of the scene. As I understand it.