Responses

I think...
1st because she is not the female lead.. i mean how can she ignore that part if she's living in a noble and that guy is the male lead and she is just a bystander
2nd I think it's because she's afraid of being rejected. Or something like, being like then afterwhile get dissapoint at her then leave her. If she still think that theduke is a male lead destined with the female lead, then more or less, if she accept the marriage there's a possibility that sooner or later the duke will fall with the real female lead. What will happen to her then?
Just my own perception
Someone explain why she doesn't wanna marry the blonde hottie again?