The quick change in Fu Ting's attitude wasn't unfounded.
Previously Xiao chen had advantage over her because he know about her perverted hobby beforehand.
But After discovering a new side of her and the advantage Xiao chen had over Fu ting disappeared.
Now Situation has turned favourable for
Fu ting.
Now Under the influence of [Son complex] identifying Xiao chen, Fu ting had developed adoration and wants to spoil Xiao chen more.
The requirement for awakening her [Son complex] are two things.
One was that Fu ting had wished to become Mother of a person.
Second was that if she developed some thoughts which a mother shouldn't have in her mind.
When Xiao chen asked her to undress,
Fu ting was still hesitating in her heart but As she saw new side of Xiao chen, she felt the need to spoil him.