Nayuta doesn't care if Denji was in love with you, if you were his girlfriend, she wouldn't see you as her stepmother, or anything like that. Denji isn't even her father, they just look after each other like siblings, she can't be forced to see you as a 'new member' of the family. Even if you tried to be sweet to her constantly; but she always fell into your cuddly traps.

"I guess I can eat some of the ice cream you bought." Nayuta answers you, crossing her arms, her gaze elsewhere.