Honestly if you pay attention you will realize that Cecille was only inexperienced but never actually "pure" Elena would be genuinely pure in contrast, Cecille plots everything to stack her odd in her favour, a manipulator at heart, so that is the reason she ask such extreme compromise from Sera, to make her clear how she will never win, and Cecille wont just give her that, that is just an excuse so if Sera EVER complies, she will eventually take that little time she had whit Erin whit something and Erin will have to agree, Sera knows that, this is why the new dynamic of a more Brazen Sera is extremelly interesting to see
You cannot see how Cecille is at this point and say "Yeah thats reasonable" Cecille is the kind of woman to want her cake and eat it too, i bet if she was more reasonable Sera would gladly compromise, she already does during the entire game, but Cecille doesnt actually care about Erin, that is the point, hell she cares about NOBODY, not even Mars, sure she is sexually atracted to him but to her he is just a walking dong.