Why Su Li-zhen does not accept Mr.Chow's offering?

Yes. Its because of the 'Ethic of time and place'

Su loves Chow as much as Chow loves Su.
Then why she rejects to go Singapur with him?
She did want to be with him - she rushed over to 2046 room before he left for Singapore but he had already left. He thought she didn't want to run away with him.

Why she didn'talk when she call in chow's room in Singapur?
She wanted to but no matter what she says, she can't be with him so she just kept quiet and miss him silently.

What is the matter which prevent her from confess her love and go with him?
She has trouble communicating her feelings. In another scene in the dark Road, she was coy and flirting but she couldn't get herself to ask him to stay overnight with her. They had to rehearsed her husband's confession of cheating on her and the lovers break-up. She wouldn't leave her husband anyway, she is that loyal to the marriage.

Loves also her husband? Ethic of time and place?
She was loyal to her husband but she fell in love with Chow.

She's also not the type that will take action because of feelings only. Maybe time and place too.