I also am very curious, every time I romance Gisette, even if I soften her twice and soften him every chance, Gisette says no. Maybe we need to be immoral? I have not tried that at all.
I also heard you get an extra dialogue option when you talk to her in week 7 is soften her 3 times, according to the Peace to Revaire guide. But I only know the "Capable of change" choice in week 5 and "Worry about others" (with high persuasion) in week 4. What else should we do